In the realm of precision engineering and industrial maintenance, the achievement of exact tolerances and perfect component alignment is fundamental to operational integrity and efficiency. While advanced manufacturing processes provide a high degree of accuracy, microscopic inconsistencies and unavoidable gaps can compromise the performance and lifespan of critical machinery. It is in this context that shims serve as indispensable tools, compensating for these gaps and enabling precise spatial adjustments. These seemingly minor components play a crucial role in ensuring that complex assemblies function as designed, thereby preventing premature wear and potential system failure.
The selection of an appropriate shim is therefore not a trivial matter but a critical decision dictated by material properties, environmental factors, and load requirements. Steel, valued for its strength, durability, and resistance to compression, is a preferred material for a vast range of demanding applications. This guide provides a comprehensive analysis to help professionals identify the best steel shims & shim stock for their specific needs. By examining key product features, material grades, and essential purchasing criteria, this resource aims to equip readers with the knowledge necessary to make an informed choice that ensures optimal performance and reliability.
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An Analytical Overview of the Steel Shim & Shim Stock Market
The market for steel shims and shim stock is a cornerstone of modern industrial and mechanical engineering, providing the critical precision required for aligning, spacing, and leveling components in machinery and structures. The global industrial shim market is experiencing steady growth, projected to expand at a CAGR of approximately 4.5% through the end of the decade, driven by increased manufacturing and construction activity worldwide. Key trends shaping the industry include a significant shift towards stainless steel variants, particularly 300 series grades, for their superior corrosion resistance in harsh environments. Furthermore, there is a rising adoption of color-coded plastic-coated or pre-laminated steel shim stock, which simplifies thickness identification and reduces the risk of error during assembly, enhancing both efficiency and accuracy on the factory floor.
The fundamental benefits of steel shims are rooted in their material properties, which offer unmatched performance in demanding applications. Steel provides exceptional compressive strength, ensuring that shims do not deform or fail under heavy loads, a common requirement in heavy machinery, power generation turbines, and structural foundations. Materials like blue tempered and hardened C1095 spring steel offer excellent wear resistance and durability, while stainless steel grades such as 304 and 316 provide vital protection against oxidation and chemical corrosion. This inherent toughness and thermal stability make steel shims the default choice for applications where long-term reliability and minimal maintenance are paramount, far surpassing the capabilities of plastic or brass alternatives in high-stress scenarios.
Despite their widespread use, the steel shim market is not without its challenges. The primary difficulty lies in maintaining material quality and manufacturing precision. Achieving tolerances as tight as ±0.0001 inches requires sophisticated manufacturing processes and stringent quality control, factors that can significantly impact cost and availability. For procurement managers and engineers, the challenge is to consistently source the best steel shims & shim stock that not only meets these tight dimensional specifications but also comes with verifiable material certifications to guarantee metallurgical integrity. Using an incorrect or substandard steel type can lead to premature component failure, galvanic corrosion when paired with dissimilar metals, or compromised performance in extreme temperature applications, posing significant operational risks.
Looking forward, the evolution of the steel shim industry will be heavily influenced by advancements in manufacturing technology and the increasing demands of high-tech sectors. Techniques such as laser cutting and photochemical etching are enabling the production of shims with highly complex geometries and burr-free edges, which are essential for sensitive applications in the aerospace, automotive, and medical device industries. As equipment designs become more compact and performance expectations rise, the need for precisely engineered steel shims will only intensify. This continued demand ensures that the market will remain dynamic, with a sustained focus on material innovation, micro-manufacturing precision, and customized solutions to meet the ever-stricter requirements of modern engineering.
5 Best Steel Shims & Shim Stock
Precision Brand C1010 Full Hard Steel Shim Stock Assortment Pack
This assortment pack consists of sheets fabricated from 1008-1010 low carbon, cold-rolled steel, tempered to a full hard condition. The material possesses a typical Rockwell hardness of B80-B90, providing good resistance to compression without being overly brittle. The standard pack includes multiple sheets, commonly in 6 x 12 inch dimensions, covering a thickness range from 0.001 to 0.032 inches. Each sheet is clearly marked with its thickness for rapid identification. The specified thickness tolerance is generally within +/-10% of the nominal thickness, which is standard for general-purpose shim stock and suitable for a wide array of industrial alignment and spacing applications. The packaging is designed for workshop convenience, often featuring a sturdy cardboard dispenser that organizes and protects the individual sheets.
In terms of performance, the Precision Brand assortment provides a reliable and cost-effective solution for routine maintenance, repair, and operations (MRO) tasks. The full hard temper ensures the shims resist deformation under moderate static loads, making them effective for machinery alignment and tool and die spacing. The low carbon steel is easily cut, stamped, or drilled with standard tooling, offering high versatility for creating custom-fit shims. While it lacks the corrosion resistance of stainless steel or the spring-back of tempered spring steel, its value proposition is excellent for general-purpose applications in controlled environments. For workshops and field service kits requiring a broad selection of common thicknesses at a low per-unit cost, this product offers an optimal balance of performance and economy.
Martin Sprocket & Gear Slotted Steel Shims
Martin’s pre-cut slotted shims are engineered specifically for machinery alignment tasks, such as adjusting motors, pumps, and generators. Manufactured from corrosion-resistant, low-carbon steel, these shims are typically zinc-plated to enhance durability in industrial environments. They are available in standardized sizes (A, B, C, D, etc.) corresponding to NEMA motor frame dimensions, with slot widths designed to accommodate standard bolt sizes. Each shim is permanently etched with its thickness and size designation, eliminating guesswork and measurement errors during installation. The manufacturing process ensures uniform thickness and deburred edges, which contributes to safer handling and more precise, stackable alignment.
The primary performance advantage of Martin slotted shims lies in their significant reduction of labor time and improvement in alignment accuracy. By eliminating the need for technicians to hand-cut shims from stock, the installation process is expedited, minimizing equipment downtime. The standardized shapes ensure a perfect fit around mounting bolts, providing full bearing support and preventing the “soft foot” condition that can arise from improperly sized shims. While the cost per shim is higher than that of raw shim stock, the value is realized through increased operational efficiency, reduced labor costs, and the enhanced reliability and longevity of the aligned machinery. For maintenance professionals, these pre-cut shims represent a best practice for repeatable, precise, and efficient equipment alignment.
McMaster-Carr 1095 Blue Tempered Spring Steel Shim Stock
This shim stock is fabricated from 1095 high-carbon steel, which is hardened and tempered to achieve a spring-like quality. It features a characteristic blue oxide finish that provides minor corrosion resistance and acts as a visual identifier. The material typically exhibits a Rockwell hardness of C48-51, endowing it with high tensile strength and an excellent elastic limit, allowing it to return to its original shape after significant deflection. It is supplied in rolls, commonly in 6 or 12 inch widths and lengths of 50 or 100 inches, with available thicknesses ranging from 0.001 to 0.062 inches. Thickness tolerances are held to a high standard, often more stringent than general-purpose carbon steel shims, making it suitable for precision applications.
The performance of 1095 blue tempered steel is defined by its resistance to wear and fatigue. It is the material of choice for applications requiring resilience and the ability to withstand cyclic loading, such as flat springs, retaining clips, wear plates, and custom tooling. Its hardness makes it more challenging to cut and form than softer steels, necessitating the use of hardened shears or abrasive cutting methods. The value of this shim stock is in its specialized mechanical properties. While its cost is greater than low-carbon steel, it is indispensable for manufacturing components that require a combination of hardness, toughness, and elasticity. For design engineers and toolmakers creating dynamic parts or high-wear surfaces, this material provides a reliable and durable solution.
Starrett 667 Series Thickness Gage / Feeler Stock
The Starrett 667 Series is a premium-grade product used for applications demanding the highest level of dimensional accuracy. While marketed as feeler gage stock, its precision makes it an exemplary choice for critical shimming tasks. It is made from high-quality, high-carbon steel and is supplied in 1/2 inch wide by 25-foot long rolls, each housed in a rewindable dispenser case for protection and convenience. Starrett manufactures this stock to exceptionally tight tolerances, for instance, a 0.0015 inch thick piece has a specified tolerance of +0.00007 / -0.00004 inches. Each roll is clearly marked with its nominal thickness, and its consistent, smooth finish ensures accurate measurements and stacking.
In performance, the Starrett 667 stock provides unparalleled accuracy and reliability. Its primary application is in metrology and precision assembly, such as setting gaps in tool and die work, calibrating fixtures, and shimming sensitive optical or electronic components where tolerance accumulation must be minimized. The dispenser case prevents kinks and damage to the thin material, preserving its flatness and accuracy. The value of this stock lies in its certification-level precision. The premium price is justified for any application where measurement error or spacing variance is not permissible. It is less a commodity shim material and more a precision instrument, representing a sound investment for quality control departments, R&D labs, and high-precision manufacturing environments.
Grainger Approved 300 Series Stainless Steel Shim Stock
This shim stock is produced from a 300-series stainless steel alloy, typically 302 or 304, and is tempered to a full hard condition. This material composition provides excellent corrosion resistance, making it suitable for use in wet, caustic, or sanitary environments. Its austenitic structure renders it largely non-magnetic, which is a critical feature for applications in electronics or near magnetic sensors. Available in assorted sheet packs or rolls, this stock comes in a comprehensive range of thicknesses, usually from 0.0005 to 0.031 inches. The full hard temper (typically Rockwell C35-45) ensures good durability and resistance to compressive forces while maintaining the inherent properties of the stainless alloy.
The performance of 300-series stainless steel shims is superior to carbon steel in any application where exposure to moisture, chemicals, or extreme temperatures is a factor. It will not rust or degrade, preventing contamination and ensuring long-term structural integrity in challenging settings like food processing plants, marine equipment, and chemical facilities. While its hardness and toughness make it more difficult to machine or stamp than low-carbon steel, its durability justifies the additional effort. The value proposition is clear for specialized industries; the higher material cost is a necessary investment to ensure compliance with sanitary standards, prevent equipment failure due to corrosion, and extend the service life of assemblies in harsh conditions.
The Critical Role of Steel Shims & Shim Stock in Modern Industry
Steel shims and shim stock are fundamental components used across a vast range of industries, from manufacturing and construction to automotive and aerospace engineering. Their primary purpose is to fill small gaps or spaces between objects, ensuring precise alignment, proper spacing, and level surfaces. A shim is a thin, often tapered or wedged piece of metal used to compensate for manufacturing tolerances, wear on parts, or surface imperfections. Shim stock, which comes in rolls or sheets of precisely calibrated thicknesses, provides the raw material for creating custom shims on-site. The inherent strength, durability, and resistance to compression of steel make it the preferred material for applications where maintaining exact tolerances under significant load or stress is essential for operational integrity and safety.
The practical need for the best steel shims is driven by the demand for precision in mechanical and structural systems. In rotating machinery such as motors, pumps, and turbines, even a few thousandths of an inch of misalignment can cause excessive vibration, leading to premature bearing failure, seal damage, and increased energy consumption. High-quality, burr-free shims with exacting thickness tolerances are critical for achieving the precise alignment required to prevent these issues. Similarly, in structural applications, shims ensure that loads are distributed evenly across support surfaces, preventing stress concentrations that could lead to structural failure. The use of inferior or imprecise shims would defeat the purpose of the alignment process, introducing new errors and compromising the long-term performance and reliability of the equipment.
Material integrity is another crucial practical factor. The “best” shim stock is defined not just by its dimensional accuracy but also by its material composition and quality. Different applications demand specific types of steel; for instance, 300-series stainless steel is used in corrosive environments like food processing or marine settings, while high-carbon steel is chosen for its hardness and strength in heavy industrial machinery. Sourcing top-tier shim stock guarantees that the material is free from defects, has been properly annealed for workability, and possesses the certified chemical and mechanical properties required for the application. This ensures the shim will not compress, corrode, or fail under operational stress, providing a stable and durable solution that maintains precision over the entire service life of the assembly.
From an economic perspective, investing in high-quality steel shims and shim stock is a highly cost-effective strategy focused on preventative maintenance. While the initial cost of a premium shim is negligible compared to the value of the machinery it protects, its impact on operational costs is substantial. Proper alignment achieved with quality shims directly reduces wear on expensive components like couplings, bearings, and seals, significantly extending their lifespan and lowering replacement parts costs. Furthermore, well-aligned equipment operates more efficiently, consuming less energy and reducing utility expenses. The most significant economic benefit is the reduction in unscheduled downtime, as machinery failures due to misalignment can halt production for hours or days, resulting in massive revenue loss that far exceeds the minor investment in proper alignment tools.
Finally, the use of the best steel shims is an exercise in efficiency and risk mitigation. For maintenance technicians and engineers, working with precisely manufactured, clearly marked, and burr-free shims streamlines the alignment process, saving valuable labor hours. There is no time wasted on de-burring, measuring, or compensating for inconsistent, low-quality materials. Economically, this translates to more productive maintenance operations and faster turnarounds. More importantly, it mitigates the significant financial and safety risks associated with equipment failure. In critical industries like power generation, aerospace, and oil and gas, using certified, reliable components is non-negotiable. High-quality shims ensure that a small, inexpensive part is not the weak link in a complex and costly system, thereby protecting assets, personnel, and the company’s bottom line.
Understanding Steel Grades and Their Impact on Performance
When selecting steel shims, it is crucial to understand that not all “steel” is created equal. The specific grade and type of steel have a direct and significant impact on the shim’s performance, durability, and suitability for a given application. The two primary categories you will encounter are carbon steel and stainless steel. Carbon steel, often a low-carbon variety like 1008 or 1010, is valued for its high strength, rigidity, and excellent hardness. This makes it ideal for high-load applications where maintaining precise thickness under significant compressive force is the top priority. However, its major drawback is its susceptibility to rust and corrosion when exposed to moisture or corrosive chemicals. Therefore, carbon steel shims are best suited for dry, climate-controlled indoor environments, such as in tool and die setups or machinery alignment within a protected factory setting.
On the other hand, stainless steel is an alloy that contains a minimum of 10.5% chromium, which forms a passive, self-repairing oxide layer on the surface, providing exceptional corrosion resistance. The most common grades for shims are 304 and 316. Grade 304 stainless steel is a versatile, general-purpose choice that offers excellent resistance to a wide range of atmospheric and chemical corrosives. It is the workhorse for applications in food processing, pharmaceuticals, and general outdoor use. Grade 316 stainless steel includes molybdenum in its alloy, which provides superior resistance to chlorides, such as saltwater and de-icing salts. This makes 316 the mandatory choice for marine environments, chemical processing plants, and any application where exposure to harsh, specific corrosives is expected.
The mechanical properties of the steel grade are just as important as its chemical resistance. Hardness, often measured on the Rockwell scale, dictates how well a shim resists indentation and deformation. A harder shim will maintain its integrity and specified thickness more reliably under load, which is paramount for precision alignment tasks. Tensile strength indicates the maximum stress the material can withstand before breaking. While shims are primarily under compression, high tensile strength is an indicator of overall material toughness and quality. When selecting a shim, you must balance the need for corrosion resistance with the mechanical demands of the job. Choosing an expensive, highly resistant 316 stainless shim for a dry, indoor application may be unnecessary, while using a carbon steel shim in a wet environment is a recipe for premature failure and loss of alignment.
Ultimately, the choice of steel grade is a technical decision based on a thorough analysis of the operating environment and the mechanical loads involved. For critical machinery alignment, where vibration and heavy loads are present, a high-strength, hard carbon steel or a robust stainless steel is essential to prevent shim extrusion or compression. For applications involving exposure to the elements, sanitation requirements, or chemical agents, the superior corrosion resistance of stainless steel is non-negotiable. A professional approach involves matching the shim material properties directly to the documented service conditions to ensure long-term reliability and precision of the assembly.
Key Industrial Applications and Use Cases
The fundamental purpose of a steel shim is to fill a small gap or space between two objects, ensuring precise alignment, clearance, or support. This simple function is critical across a vast spectrum of industrial, commercial, and technical fields where tight tolerances are paramount. One of the most common and critical applications is in the alignment of rotating machinery, such as electric motors, pumps, fans, compressors, and turbines. Misalignment between a motor and the equipment it drives is a leading cause of premature bearing failure, seal damage, increased vibration, and excessive energy consumption. Pre-cut, slotted steel shims are used under the feet of the motor to precisely adjust its vertical and angular position, bringing it into perfect alignment with the driven component. The high compressive strength of steel ensures these alignment corrections remain stable over time, even under heavy operational loads and vibration.
In the tool and die industry, steel shims and shim stock are indispensable for the manufacturing of precision components. Die makers and machinists use them to accurately set the clearance between a punch and a die in a stamping press. This clearance is critical as it determines the quality of the cut edge on a metal part and affects the longevity of the tooling itself. Similarly, in injection molding, shims are used to align mold halves and adjust the positioning of inserts and cores. In these applications, machinists often use rolls of shim stock, which can be cut and shaped to create custom-fit shims for unique geometries, providing a level of precision that standard parts cannot match.
The automotive and aerospace sectors rely heavily on steel shims for both manufacturing and maintenance. In automotive repair, shims are used to set the correct gear mesh patterns in differentials, adjust camshaft timing, and correct suspension caster and camber angles. In aerospace assembly, they are used to manage tolerance stack-up in airframes, ensuring a precise fit between structural components like wing spars and fuselages. In these safety-critical applications, the material consistency, certified thickness tolerance, and reliability of the steel shim are absolutely essential. The ability of a steel shim to withstand extreme temperature fluctuations and mechanical stresses makes it the only viable choice for many of these demanding uses.
Beyond manufacturing and vehicles, steel shims find broad use in construction and plant maintenance. They are used to level structural steel beams, support and align precast concrete panels, and set the foundation for heavy industrial equipment. In power plants and refineries, maintenance crews use shims to realign equipment during planned outages, ensuring operational efficiency and safety. In essence, anywhere that two or more components must be joined or positioned with an accuracy measured in thousandths of an inch, steel shims provide the simple, reliable, and robust solution. Their versatility ranges from micro-adjustments in delicate scientific instruments to supporting multi-ton machinery, making them a cornerstone of modern engineering.
Best Practices for Shim Installation and Handling
Achieving a truly precise and stable alignment with steel shims goes beyond simply selecting the right product; it requires a meticulous and disciplined installation process. The first and most critical step is surface preparation. The surfaces of both the machine foot and the baseplate or foundation must be impeccably clean. Any dirt, grease, rust, paint, or old gasket material will create a “soft” interface, compromising the accuracy of the shimmed height. Furthermore, it is essential to check for and remove any burrs, nicks, or high spots using a flat file or deburring stone. A single small burr can hold the machine foot artificially high, invalidating the entire alignment process. A final wipe with a solvent ensures no oily residue remains. This foundational step is non-negotiable for professional results.
A key best practice involves the management of the shim stack itself. While it might seem logical to use many very thin shims to creep up on a measurement, this should be avoided. A stack composed of numerous thin shims can act like a leaf spring, introducing a spongy, unstable soft foot condition that is difficult to diagnose. The professional standard is to use the fewest number of shims possible to achieve the required thickness. A widely accepted rule of thumb is to limit any single shim stack to a maximum of three or four shims. When building the stack, it is also advisable to place the thickest shim on the bottom, against the base, and the thinnest shim on the top, directly under the machine foot. This configuration provides the most stable support structure.
Proper handling and placement are equally important for a successful installation. Due to their manufacturing process, steel shims and shim stock have extremely sharp edges that can easily cause severe cuts. Technicians should always wear appropriate cut-resistant gloves when handling them. When inserting the shims, particularly pre-cut slotted shims, they must be pushed fully into position so that the mounting bolt does not rest on the shim, but passes freely through the slot. The shim must provide broad support across the machine foot’s surface area. Incomplete insertion or using a shim that is too small for the foot concentrates the load on a small area, leading to deformation and loss of alignment.
Finally, the process of shimming is iterative and requires verification at every stage. After an initial “rough” alignment, measurements are taken with tools like dial indicators or laser alignment systems to determine the required shim thickness. After the calculated shims are inserted, the mounting bolts should be tightened in a specific sequence to a preliminary torque value. The alignment must then be re-measured to verify that the correction was successful. It is common for adjustments to be needed, requiring the addition or removal of shims. This methodical process of measuring, correcting, and verifying is the only way to ensure that the final alignment is within the specified tolerance and will remain stable throughout the machine’s operational life.
Steel Shims vs. Alternative Materials: A Comparative Analysis
While steel is the most common and versatile material for shims, it is not the only option available. A comprehensive understanding of the alternatives is essential for selecting the optimal material for a specific task. The primary alternatives include plastic, brass, and aluminum, each with a unique profile of advantages and disadvantages when compared to steel. The decision to use an alternative material is typically driven by factors such as corrosive environment, electrical conductivity requirements, concerns about damaging mating surfaces, or weight limitations.
Plastic or polymer shims are a popular alternative in certain applications. Their most significant advantage is their complete immunity to corrosion and their non-conductive nature, making them ideal for use in wet environments or for electrically isolating components. Many plastic shim kits are also color-coded by thickness, which can significantly speed up the selection process. However, their primary weakness is a much lower compressive strength compared to steel and a susceptibility to “creep,” which is the tendency to slowly deform over time under a sustained load. This makes them unsuitable for aligning heavy, high-vibration machinery, but an excellent choice for lighter-duty tasks like leveling construction components, aligning window and door frames, or for non-critical motor alignment where loads are minimal.
Brass shims offer a unique middle ground. Brass is an alloy of copper and zinc that provides good corrosion resistance, superior to that of carbon steel though generally less than stainless steel. A key property of brass is that it is softer than steel. This can be a distinct advantage in applications involving delicate or precision-machined surfaces, as a brass shim is less likely to mar or scratch the mating component if movement occurs. Additionally, brass is non-sparking, a critical safety feature for use in explosive or flammable atmospheres, such as in oil and gas facilities or grain elevators. The trade-off is that brass has lower compressive strength and a lower melting point than steel, and it is typically more expensive.
Aluminum shims are another option, valued primarily for their light weight and good corrosion resistance. They are easy to cut and form, making them suitable for creating custom shapes from shim stock. However, aluminum is a relatively soft metal with significantly less strength and hardness than steel. It is therefore reserved for low-load, static applications where weight is a primary concern, such as in certain aerospace or custom automotive assemblies. Ultimately, the comparison reinforces steel’s position as the default choice for the majority of industrial shimming tasks. Steel’s unparalleled compressive strength, hardness, and dimensional stability under thermal and mechanical stress make it the only reliable option for precision alignment of heavy, critical, and dynamic machinery where long-term reliability is the paramount concern.
A Comprehensive Buying Guide: How to Select the Best Steel Shims & Shim Stock
In the world of precision engineering, manufacturing, and industrial maintenance, success is often measured in thousandths of an inch. It is in this microscopic realm that steel shims and shim stock serve as indispensable components. These thin sheets of metal are the unsung heroes of mechanical alignment, gap compensation, and tolerance stacking, ensuring that machinery from colossal turbines to delicate scientific instruments operates with the accuracy and longevity for which it was designed. Whether compensating for wear in a motor base, setting the precise clearance in a stamping die, or aligning complex aerospace assemblies, the function of a shim is fundamentally critical. However, the apparent simplicity of a shim belies a complex set of material and dimensional properties that dictate its performance. Selecting the incorrect shim can lead to premature equipment failure, costly downtime, and compromised safety.
This guide is designed to demystify the selection process for steel shims and shim stock. The market offers a vast array of options, varying in material composition, hardness, thickness, tolerance, and format. Navigating these choices requires a clear understanding of the application’s specific demands. We will move beyond a superficial overview to provide a detailed, analytical framework for your purchasing decision. By examining six key factors—from the metallurgical nuances of steel alloys to the practical implications of format and certifications—this guide will equip engineers, procurement specialists, and maintenance professionals with the knowledge to confidently specify and procure the ideal shimming solution. The objective is to transform the act of buying a shim from a simple commodity purchase into a calculated engineering decision, ensuring optimal performance, reliability, and value for any application.
1. Material Grade and Alloy Composition
The foundational decision in selecting a shim is its material composition, which directly governs its strength, corrosion resistance, and cost. The two primary categories are carbon steel and stainless steel, each with distinct advantages. Carbon steel, typically a low-carbon variety like C1008 or C1010, is prized for its high tensile strength, excellent wear resistance, and economic value. With a typical tensile strength in the range of 45,000 to 65,000 PSI (pounds per square inch), carbon steel shims provide robust support and resist compression under heavy static loads, making them ideal for general-purpose machinery alignment, tool and die setting, and structural applications where the environment is controlled. The primary drawback, however, is its low resistance to corrosion. Unprotected carbon steel will readily rust when exposed to moisture and oxygen, necessitating a dry environment or the application of a protective coating like oil or zinc plating, which adds an extra step and potential point of failure.
For applications demanding superior longevity in corrosive or challenging environments, stainless steel is the unequivocal choice. The most common alloy for shims is Type 304 stainless steel, an austenitic grade containing approximately 18% chromium and 8% nickel. This composition creates a passive chromium-oxide layer on the surface, providing excellent resistance to a wide range of atmospheric and chemical corrosives. For more aggressive conditions, such as marine environments, chemical processing plants, or areas exposed to de-icing salts, Type 316 stainless steel is specified. The addition of 2-3% molybdenum to its composition grants it superior resistance to pitting and crevice corrosion caused by chlorides. While stainless steel shims come at a premium price compared to carbon steel, the investment is often justified by reduced maintenance and enhanced equipment reliability in critical or exposed applications. Other grades, like the harder Type 301, are also used when a spring-like quality is required.
2. Precision Thickness and Tolerance Standards
The defining characteristic and primary function of a shim is its thickness. The ability to introduce a precise, known dimension into an assembly is what makes shims so valuable. Steel shims are available in a vast spectrum of standard thicknesses, commonly ranging from as thin as 0.0005 inches (0.0127 mm) to over 0.250 inches (6.35 mm). However, the nominal thickness is only part of the story; the manufacturing tolerance is what separates a standard washer from a precision shim. Tolerance refers to the permissible deviation from the stated nominal thickness. A shim with a thickness of 0.010″ and a tolerance of +/- 0.001″ could measure anywhere between 0.009″ and 0.011″. For high-precision applications like aligning motor bearings or setting gear backlash, this variance can be unacceptable.
Therefore, scrutinizing the tolerance specification is paramount. Reputable manufacturers produce shims to specific industry standards, such as ASTM A109 for carbon steel and ASTM A480 for stainless steel, which dictate acceptable thickness tolerances. For instance, a standard tolerance for a 0.005″ thick shim might be +/- 0.0005″, while a higher-precision (and higher-cost) version could offer a tolerance of +/- 0.0002″. When evaluating suppliers, always demand clear tolerance data. Sourcing the best steel shims & shim stock often means matching the tolerance level precisely to the engineering specifications of the project. Paying for a tighter tolerance than necessary increases cost, while using a shim with a tolerance that is too wide can negate the very purpose of the alignment, leading to vibration, accelerated wear, and eventual failure.
3. Hardness, Temper, and Ductility
The hardness of a steel shim determines its ability to resist permanent deformation (plasticity) and surface indentation under compressive load. It is a critical factor for durability, especially in dynamic applications or where the shim is subjected to high stress. Hardness is typically measured on the Rockwell scale (HRB for softer steels, HRC for harder steels). Shim stock is produced in various tempers, which are achieved through cold rolling and/or heat treatment processes. Common tempers include annealed (soft), quarter-hard, half-hard, and full-hard. An annealed shim is soft and ductile, making it easy to bend, form, or cut into custom shapes without fracturing. However, it will deform more easily under load. A full-hard shim, conversely, offers maximum resistance to compression and wear but is brittle and may crack if subjected to significant bending.
The choice of temper is a direct trade-off between formability and compressive strength. For shims that must be fitted around a curved surface or custom-trimmed on-site, a softer temper like quarter-hard or half-hard (typically 75-85 HRB) provides a good balance. For applications involving purely static, high-load compression, such as supporting the base of a heavy press, a full-hard temper (often >85 HRB or into the HRC scale) is essential to prevent the shim from being crushed over time, which would lead to a loss of alignment. For example, a full-hard C1095 “blue-tempered” shim stock can reach a hardness of 45-51 HRC, making it extremely durable but only suitable for flat applications. In contrast, an annealed 304 stainless steel shim might have a hardness of only 75 HRB, offering excellent ductility for complex forming.
4. Format: Pre-Cut Slotted Shims vs. Rolled Shim Stock
The physical format in which you purchase shimming material has significant practical implications for labor cost, efficiency, and safety. Pre-cut slotted shims are manufactured to standardized dimensions, most commonly for aligning the feet of motors, pumps, and generators. These shims, often sold in assorted kits, feature a slot that allows them to be slipped into place around an already-installed anchor bolt without needing to lift the equipment completely off its base. This drastically reduces installation time and labor. Standard shapes (e.g., A, B, C, D) correspond to NEMA motor frame sizes, ensuring a perfect fit. Furthermore, pre-cut shims are professionally deburred, eliminating the dangerously sharp edges that result from hand-cutting, thereby improving workplace safety. For routine maintenance, repair, and operations (MRO), pre-cut shims offer unparalleled convenience and consistency.
On the other hand, rolled shim stock offers maximum versatility. It is supplied in rolls of a specific width (e.g., 6″, 12″) and length (e.g., 50″, 100″, 300″), allowing technicians to fabricate custom-sized and shaped shims for unique or one-off applications. This is ideal for prototyping, tool and die making, or shimming large, non-standard machinery where pre-cut sizes are not available. Purchasing in roll form can be more cost-effective on a per-square-inch basis, especially for high-volume users who can nest parts efficiently to minimize scrap. The trade-off is the requirement for additional labor and specialized tools (like metal shears or snips) to cut the stock to size. This process introduces variability and the aforementioned safety risk from sharp edges if not handled with care. The decision hinges on a cost-benefit analysis: the time-saving and safety benefits of pre-cuts versus the flexibility and material cost savings of rolled stock.
5. Corrosion Resistance and Surface Finish
While material grade provides the primary defense against corrosion, a deeper look at the specific corrosive agents and the shim’s surface finish is warranted for critical applications. The choice between 304 and 316 stainless steel, for example, should be data-driven. Type 304 is sufficient for general humidity, freshwater, and most food processing environments. However, if the shim will be exposed to saltwater spray, bleach, or other chloride solutions, the molybdenum in Type 316 provides a quantifiable increase in protection against pitting corrosion, with a Pitting Resistance Equivalent Number (PREN) of ~25 compared to ~19 for Type 304 (higher is better). For carbon steel shims, specifying a protective coating is an option. A zinc electroplate can provide sacrificial protection in mildly corrosive atmospheres, while a heavier hot-dip galvanization (though less common for thin shims) offers more robust coverage. It is also crucial to consider galvanic corrosion, which can occur when the steel shim is in contact with a dissimilar metal (e.g., an aluminum housing) in the presence of an electrolyte, a factor that may steer the choice towards a more compatible stainless steel grade.
The surface finish of the shim, while often a secondary consideration, can impact performance in specialized scenarios. The standard finish for most shim stock is a “2B” mill finish, which is smooth and moderately reflective. For applications requiring a higher degree of cleanliness or a slightly improved corrosion resistance, a “BA” (Bright Annealed) finish is available. This highly reflective, mirror-like finish is created by heat-treating the steel in a controlled, oxygen-free atmosphere. The resulting surface is smoother and less porous, making it easier to clean and offering fewer initiation sites for crevice corrosion. In sanitary applications, such as in the pharmaceutical or food and beverage industries, a smooth, non-porous surface finish may be mandated by regulation to prevent bacterial colonization, making the BA finish a functional requirement rather than an aesthetic choice.
6. Application-Specific Properties and Certifications
Beyond the common factors, many advanced applications impose unique requirements that must be addressed during procurement. One such property is magnetism. Standard austenitic stainless steels like 304 and 316 are non-magnetic in their fully annealed state. However, the cold-rolling process used to achieve higher tempers and thinner gauges induces a phase transformation (austenite to martensite), which can make the material slightly magnetic. For applications involving sensitive electronic sensors, MRI equipment, or particle accelerators, this induced magnetism can be disruptive. In such cases, specifying “annealed” or “non-magnetic” material is critical. Conversely, ferritic stainless steels (e.g., Type 430) are inherently magnetic and may be chosen for that property. Another key property is the coefficient of thermal expansion. In assemblies that experience significant temperature fluctuations, the shim material should ideally have a thermal expansion rate similar to the components it is aligning (e.g., a steel shim for a steel housing) to maintain tight tolerances across the operating temperature range.
Finally, for regulated industries such as aerospace, defense, medical, and nuclear, material certifications are not optional—they are mandatory. A Certificate of Conformance (CofC) is a basic document stating the product meets the required specifications. A far more rigorous document is the Material Test Report (MTR) or Certified Mill Test Report (CMTR), which provides a detailed “birth certificate” for the metal, listing its exact chemical composition and measured physical properties (like tensile strength and hardness) traced back to a specific heat lot. For government and defense contracts, compliance with DFARS (Defense Federal Acquisition Regulation Supplement) may be required, ensuring the specialty metals are sourced from qualifying countries. For products destined for the European market, RoHS (Restriction of Hazardous Substances) compliance, which certifies the material is free of lead, mercury, and other specified substances, is often necessary. Verifying that a supplier can provide the required level of documentation is a crucial final step in the procurement process for any critical application.
Frequently Asked Questions
What is the fundamental difference between a pre-cut steel shim and a roll of steel shim stock?
The primary distinction lies in their form and intended use. A pre-cut steel shim is a finished component, manufactured to a specific shape, size, and thickness, ready for immediate installation. These are often produced with slots and holes (e.g., U-shaped motor shims) designed for standardized applications, such as aligning motors, pumps, and other rotating equipment. Their main advantage is convenience and speed, as they eliminate the need for on-site fabrication, reducing labor time and ensuring dimensional consistency across repetitive tasks.
In contrast, steel shim stock is a raw material, typically supplied in rolls or flat sheets of a specific thickness. It offers maximum versatility, allowing technicians to cut, punch, or shape a shim to the exact custom dimensions required for a unique application, such as prototyping, tool and die setting, or repairing non-standard machinery. While it requires more labor to prepare, shim stock is more cost-effective for workshops that face a wide variety of alignment challenges and is indispensable when a pre-cut solution is not available.
Should I choose carbon steel or stainless steel shims for my project?
The decision between carbon steel and stainless steel hinges almost entirely on the shim’s operating environment. Carbon steel, particularly low-carbon grades like 1008/1010 or high-carbon spring steel like 1095, offers excellent hardness and compressive strength at a lower cost. This makes it an ideal choice for general-purpose shimming in controlled, dry, indoor environments where exposure to moisture or corrosive agents is not a concern, such as in most manufacturing plant machinery.
Stainless steel, most commonly grades 302, 304, or 316, contains chromium, which forms a passive, corrosion-resistant layer on the surface. While typically more expensive and slightly softer than hardened carbon steel, its ability to resist rust and chemical attack is non-negotiable in specific applications. For machinery in food and beverage processing, pharmaceutical manufacturing, marine environments, or outdoor installations, stainless steel is the mandatory choice to prevent contamination and ensure long-term structural integrity against the elements.
How can I accurately determine the correct shim thickness needed for my application?
Determining the correct shim thickness begins with precise measurement of the gap. The most reliable method is to use a set of feeler gauges to find the exact spacing between the two components you need to align. For more complex alignment tasks, such as correcting a “soft foot” on a motor base, a dial indicator is used to measure the movement or distortion as bolts are loosened, directly indicating the required shim thickness. Always measure at multiple points to account for any angular misalignment.
Once you have a baseline measurement, it is standard industry practice to build up the required thickness by stacking several thinner shims rather than using a single thick one. For example, to fill a 0.025″ gap, using a 0.020″ and a 0.005″ shim is preferable to using one 0.025″ shim. This “shim stack” approach allows for fine-tuning the alignment by adding or removing a very thin shim. After the initial shims are inserted, re-measure with the dial indicator to confirm the alignment is correct and that no new stresses have been introduced into the assembly.
What are laminated shims, and what are their primary advantages?
Laminated shims, also known as peelable or peel-off shims, are engineered components made from layers of precision-gauge metal foil that are bonded together with a resin. From the outside, they look and handle like a single, solid shim. However, a user can easily peel away individual layers with a utility knife to reduce the shim’s thickness, achieving a highly precise, custom fit directly at the point of assembly. This innovative design effectively combines the adjustability of a full set of loose shims into a single, easy-to-manage part.
The primary advantages of laminated shims are significant gains in efficiency and accuracy. They drastically reduce inventory requirements, as one laminated shim can replace dozens of different individual shim thicknesses. This is a major benefit for field service technicians or maintenance departments. Furthermore, they accelerate the assembly process by eliminating the time spent fumbling with and sorting through multiple thin, loose shims. This also enhances safety and precision by preventing the accidental dropping of a shim into sensitive machinery and ensuring the entire stack stays together as a single, stable unit during installation.
When would plastic or brass shims be a better choice than steel?
While steel is the default choice for high-strength applications, plastic or brass shims are superior in specific scenarios where steel’s properties are a disadvantage. Plastic shims, often made from Mylar® or color-coded polyester, are completely immune to corrosion, are non-conductive, and have very low compressibility. This makes them the ideal choice for applications requiring electrical insulation, such as spacing electronic components, or in highly corrosive environments where even stainless steel may falter. Their color-coded thickness system also simplifies identification and prevents errors during assembly.
Brass shims are used when non-magnetic and non-sparking properties are critical. In assemblies with sensitive magnetic sensors or in explosive atmospheres (e.g., oil and gas, munitions plants), a steel shim could interfere with readings or create a dangerous spark if struck. Brass, an alloy of copper and zinc, provides good compressive strength—though less than steel—while being non-magnetic and non-sparking, making it a crucial safety component in these specialized environments. The choice of material should always consider the full range of electrical, chemical, and safety factors of the application.
What do steel grades like 304 Stainless or 1010 Carbon actually mean for a shim’s performance?
The grade of steel is a shorthand designation for its chemical composition, which directly dictates its mechanical properties like hardness, strength, and corrosion resistance. For carbon steel, the grade number often reflects its carbon content. A grade like 1010 Carbon Steel indicates a low-carbon steel (approximately 0.10% carbon), making it relatively soft, ductile, and easy to form. This grade is perfect for general-purpose, low-stress applications where high strength is not the primary requirement and cost is a factor.
For stainless steel, a grade like 304 is part of the “austenitic” family and signifies a specific alloy composition, typically around 18% chromium and 8% nickel. This high chromium content is what provides its exceptional resistance to rust and oxidation. In performance terms, a 304 stainless steel shim will not rust when exposed to water or many chemicals, making it essential for hygienic or outdoor use. In contrast, a high-carbon steel like 1095 (“Blue Tempered Spring Steel”) is much harder and holds its shape under repeated stress, but will rust quickly if not protected, making it suitable for springs and high-wear internal components, but not for corrosive environments.
How important is a steel shim’s hardness rating, often measured in Rockwell (HRC)?
The hardness rating of a steel shim is critically important as it indicates its ability to resist deformation under compressive force. Measured on scales like the Rockwell C scale (HRC), hardness is a direct measure of the material’s resistance to permanent indentation. A shim’s fundamental purpose is to maintain a precise gap between two surfaces. If a shim is too soft for the application, it will compress or “crush” under the load from bolted joints or the weight of the machine, causing the precise alignment to be lost. This leads to increased vibration, premature bearing wear, and potential equipment failure.
In practice, the required hardness depends on the load. For light-duty, static applications, a softer, low-carbon steel shim (with a Rockwell B rating) is adequate. However, for high-load applications, such as aligning the feet of a multi-ton motor or a high-torque gearbox, a full-hard, high-carbon, or hardened stainless steel shim is mandatory. These shims often have a hardness of HRC 40-50 or higher, ensuring they can withstand thousands of pounds of compressive force without yielding. Choosing a shim with an appropriate hardness rating is not just about fit; it’s about ensuring the long-term stability and reliability of the entire machine assembly.
Final Thoughts
Selecting the appropriate steel shim necessitates a systematic evaluation of material properties, dimensional accuracy, and application-specific demands. The choice between stainless steel, prized for its superior corrosion resistance in harsh environments, and carbon steel, valued for its strength and cost-efficiency, is a primary determinant of performance and longevity. Furthermore, the efficacy of any shim is contingent upon its manufacturing precision, where tight thickness tolerances and adherence to industry standards are non-negotiable for achieving the exact spacing or alignment required in critical industrial and mechanical applications. These fundamental criteria form the basis for distinguishing a standard component from a high-performance, reliable solution.
The market addresses these requirements through two primary forms: pre-cut shims for standardized tasks and versatile shim stock for custom fabrication. An in-depth analysis demonstrates that identifying the best steel shims & shim stock is less about a single superior brand and more about aligning product specifications with the intended operational context. For professionals in maintenance and repair, a comprehensive assortment kit with varied thicknesses offers the most strategic investment, ensuring readiness for diverse alignment challenges. Conversely, for high-volume manufacturing or specialized engineering projects, sourcing material to exact grade specifications and pre-cut dimensions is paramount for ensuring consistency and production efficiency. Therefore, a thorough assessment of an operation’s primary requirements—whether versatility for repair or uniformity for production—is the most critical step in procuring shims that deliver optimal performance and economic value.