ratchet-coupling

Century Dictionary and Cyclopedia

1. n. A device for uncoupling machinery in the event of a sudden stoppage of the motion of a driving-wheel, as by an obstruction. It consists of a ratchet-wheel inserted in a sleeve on the exterior shaft of a driving-wheel. The ratchet is efficient as long as it transmits the initial motion; but if the revolution of the driver is checked, the sleeve slips over the ratchet until the machinery loses its momentum, thus avoiding a shock.