A metallic item, solid or tubular, having one closed end formed to fit into a shallow recess or groove, or having a flat or concave surface used to exert pressure against a component part. It is designed for use with a spring, helical, compression, which exerts pressure to hold a shaft, pin, or the like, in a semirigid position in housings or other mechanical devices. Does not have internal or external threads. Excludes plunger, quick release. For electrical items, see detent, switch and plunger, solenoid. See also catch, friction.