Ratchet

Ratchet, toothed wheel that operates with a catch, or pawl, so as to rotate in only one direction. Typically, the toothed ratchet wheel is rotated by a handle. The pawl is curved and pivoted so that it rests on or presses against the wheel teeth. When the wheel rotates in the permitted direction, the teeth can move beneath the pawl. As soon as the rotation ceases, the pawl engages one of the wheel teeth and prevents any motion backward. A release mechanism is usually incorporated to disengage the pawl when required. The escapement in clocks and watches is an example of a ratchet.