Shim

A small piece of scrap lumber or shingle, usually wedge shaped, which when forced behind a furring strip or framing member forces it into position. Also used when installing doors and placed between the door jamb legs and 2 X 4 door trimmers. Metal shims are wafer 1 1/2" X 2" sheet metal of various thicknesses used to fill gaps in wood framing members, especially at bearing point locations.