Snap

A tool used in field riveting to form the head of the rivet. It consists of a hammer-like head on a handle and having one of its faces hollowed out to give the desired shape to the rivet head. By placing this on the hot metal and striking it with a sledge, the rivet end is forced to conform to the shape of the hollow. Also a spring catch as in a snap hook. To break suddenly with a short fracture.