escape wheel

noun Horology.

1. a toothed wheel for regulating a going train to which it is geared, engaging intermittently with the pallets of a pendulum or balance mechanism in such a way as to cause the mechanism to oscillate rhythmically, and in so doing free the going train for part of each oscillation.

noun

1. horology a toothed wheel that engages intermittently with a balance wheel or pendulum, causing the mechanism to oscillate and thereby moving the hands of a clock or watchAlso called: scapewheel