A projection on a machine part, such as a pawl for controlling the motion of a ratchet wheel in a watch escapement, that engages the teeth of a ratchet wheel to convert reciprocating motion to rotary motion or vice versa.

• 棘爪机器部件上的一个突出部分，例如在一个观察棘轮装置中控制棘轮运转的棘爪，用来衔接棘轮的齿，以将往复运动转换为旋转运动；反之亦然