RATCHET

A SAW-TOOTHED WHEEL.
THE RATCHET WHEEL IN A WATCH IS A TOOTHED WHEEL THAT IS FIXED BY A SQUARE HOLE TO THE BARREL ARBOR. A CLICK (PAWL) PREVENTS THE RATCHET WHEEL FROM TURNING IN THE UNWINDING DIRECTION.
IN A STRIKING MECHANISM, THE HOUR-RATCHET OR HOUR-RACK IS A TOOTHED SECTOR THAT LIFTS THE HAMMER TO STRIKE THE HOURS.