A plectrum, also called a pick, is a usually small, flat, often triangular or wedge-shaped tool that is used to pluck or strum some stringed instruments. Some plectra are hand held or worn on the hand, such as those used with guitars and mandolins. Others are mounted in a mechanism, such as those used in the harpsichord. Plectra have been are made from a variety of materials, including metal, wood and shell, but today the most common materials are various types of plastic. Plectra used with guitars are also called guitar picks.