SHIM

A shim is a thin, often wedge-shaped piece of material used to fill gaps, align parts, and adjust spacing in mechanical assemblies. Shims are used to achieve precise alignment or leveling when components do not fit exactly after manufacture or installation.

Common materials include metal shims (such as stainless steel or aluminum), plastic or polymer shims, and fiber or composite shims. Shapes range from rectangular bars and discs to wedge-shaped pieces, and thicknesses span from fractions of a millimeter to several millimeters.

Typical applications include leveling machinery, aligning shafts, setting bearing clearances, filling gaps in flanges, floor leveling, door alignment, and various types of assembly work where small adjustments are needed to achieve correct fit and function.

In computing, a shim is a small library or piece of code that intercepts, adapts, or augments calls to another API, providing compatibility or bridging version gaps. For example, Windows compatibility shims modify the behavior of older applications so they run on newer operating systems. Shims in software are usually designed to be transparent to the caller and to avoid changing the original code.

The term is also used broadly to describe any spacer or adapter that improves fit or interoperability without altering the underlying components. In practice, shims serve as simple, low-cost tools for precision, alignment, or compatibility across both mechanical and software contexts.