Gap-filling wedge, also known as a SHIM, is a thin piece of material used to fill in the space between two objects. It is typically used to adjust the fit of parts in a variety of applications, such as construction, engineering, and automotive repair. Shims are often made of metal, plastic, or wood, and can be cut to fit the exact size of the gap they are intended to fill. They are an important tool for ensuring that parts fit together properly and securely.