The polyester round shim has an opaque amber color to indicate 0.001" thickness, meets Federal Specification L-P-377, and has a standard tolerance. Polyester is a durable, nonconductive plastic that resists corrosion, many chemicals, and oils. The shim is color-coded for thickness identification.

Shims are thin pieces of material placed between objects for a variety of uses, including added support, improved leveling, increased insulation, tighter seals, or better spacing. They also can be used to fill gaps between machine parts that are prone to wear. Shapes include round, notched, slotted, and horseshoe.