Shims are thin pieces of material used to create precise spacing, alignment, clearance, or support between machine components. They may look simple, but they play an important role in maintaining accurate assemblies in manufacturing, automotive repair, tooling, construction, and maintenance work.
Different applications need different shim shapes, materials, and thicknesses. Choosing the right type helps prevent misalignment, vibration, uneven loading, and premature wear.
What Is a Shim?
A shim is a thin spacer installed between two surfaces to adjust their position or fit. It can be used to fill a gap, set a height, align shafts, position bearings, level machinery, or control a tolerance.
Shims are commonly made from metal, plastic, composite materials, or laminated layers. They may be supplied as individual pieces, rolls, sheets, assortments, or custom-machined parts.
Flat Sheet Shims
Flat sheet shims are among the most common types. They are supplied as thin, rectangular sheets that can be cut to the required size and shape.
They are useful for:
- Machine leveling
- Fixture setup
- Die and mold adjustment
- Bearing support
- Gap filling
- General repair work
Sheet shims are often available in stainless steel, brass, aluminum, carbon steel, and plastic. They are a flexible choice when custom dimensions are needed on-site.
Slotted or U-Shaped Shims
Slotted shims have an open slot that allows them to slide around a bolt, stud, or shaft without removing the fastener completely.
This design can reduce installation time during alignment and maintenance. Slotted shims are commonly used for motor alignment, machinery mounting, structural support, and equipment installation.
The slot width, overall dimensions, and thickness should match the fastener and load requirements.
Round Shims
A round shim is a circular spacer, often with a centre hole. It is commonly used around shafts, bolts, arbors, bearings, gears, pulleys, and rotating assemblies.
Round shims are useful when a uniform circular contact area is needed. They may also be called arbor shims, shim washers, or spacer shims, depending on the application.
Typical uses include:
- Adjusting shaft-mounted tool spacing
- Setting bearing clearance
- Positioning gears or pulleys
- Fine-tuning die buttons
- Controlling axial movement in mechanical assemblies
When selecting a round shim, confirm the inside diameter, outside diameter, thickness tolerance, material, and required load capacity.
Die Button Shims
Die button shims are precision circular shims used in stamping dies and tooling. They help control punch length, die clearance, and component position.
These shims are often sold in organized assortments with carefully controlled thickness increments. Accurate selection is important because small thickness changes can affect stamping quality and tool life.
Laminated Shims
Laminated shims are built from multiple thin metal layers bonded together. Individual layers can be peeled away to create a precise thickness adjustment.
They are helpful when exact final dimensions are not known during assembly. Instead of stocking many individual shim thicknesses, technicians can remove layers as needed.
Laminated shims are often used in aerospace, machinery assembly, tooling, and precision maintenance. The surface condition and remaining layer integrity should be checked after adjustment.
Tapered Shims
Tapered shims gradually change in thickness from one end to the other. They are useful for correcting angular misalignment, adjusting machine level, setting door or frame alignment, and creating a controlled slope between components.
Because they affect angle as well as height, tapered shims should be selected carefully. Incorrect use can create uneven loading or unwanted movement.
Horseshoe Shims
Horseshoe shims have a U-shaped profile similar to slotted shims, but are often used in construction, glazing, door installation, and framing applications. They can be placed around fasteners or between building components to provide spacing and support.
Plastic horseshoe shims are common where moisture resistance and electrical insulation are needed.
Custom-Machined Shims
Custom shims are designed for unique dimensions, complex profiles, special materials, or high-precision tolerances. They may include holes, tabs, notches, slots, curved edges, or identification markings.
Custom parts are often used in automotive, aerospace, medical-device, electronics, and high-precision industrial equipment. A technical drawing should specify thickness, tolerances, material grade, burr requirements, flatness, and finish.
Common Shim Materials
Stainless Steel
Stainless steel offers corrosion resistance and good strength. It is widely used in industrial, marine, food-processing, and outdoor applications.
Carbon Steel
Carbon steel is strong and cost-effective for dry indoor applications. It may require coating or corrosion protection in harsh environments.
Brass
Brass has good corrosion resistance and is easy to machine. It is often used in electrical, plumbing, and precision-instrument applications.
Aluminum
Aluminum is lightweight and corrosion resistant. It can be useful where low mass is important, though it may not suit high-load contact areas.
Plastic and Composite Materials
Plastic shims can provide electrical insulation, moisture resistance, chemical resistance, and low friction. Common materials include nylon, polyethylene, acetal, and composite laminates.
How to Choose the Right Shim
Before selecting a shim, consider:
- Required thickness and tolerance
- Inside and outside dimensions
- Shape and access around fasteners
- Load and contact pressure
- Exposure to moisture, chemicals, heat, or vibration
- Electrical insulation needs
- Corrosion resistance
- Surface finish and burr requirements
- Whether a custom profile is necessary
For precision assemblies, measure the actual gap and use calibrated shims rather than estimating thickness.
Conclusion
Shims come in many forms, including flat sheet shims, slotted shims, round shims, die button shims, laminated shims, tapered shims, horseshoe shims, and custom-machined parts. Each type serves a specific purpose in spacing, alignment, leveling, or tolerance control.
A properly selected round shim or other precision spacer can improve assembly accuracy, reduce wear, and support reliable equipment performance. The best choice depends on geometry, material requirements, operating conditions, and the precision needed for the job.
Post time: 07-23-2026
