Rātch'et-wheel, n.

n. (Mach.) A circular wheel, having angular teeth, by which it may be moved forward, as by a lever and catch, or pawl, into which a pawl may drop to prevent the wheel from running back.

In the cut, the moving pawl e slides over the teeth in one direction, but in returning, draws the wheel with it, while the pawl d prevents it from turning in the contrary direction;—called also, simply, a ratchet.