a transmission member for a worm gear having a thrust ring placed over the shaft of a motor . the worm gear is slip - fit over the shaft and has a coupling head with a pair of projections facing away from the motor . a coupling washer is press - fit onto the motor shaft and has a pair of projections as well , each of which is fitted with an o - ring . the coupling washer is mated to the worm gear so both sets of projections intermesh and form a torque - transmitting arrangement , with the o - rings acting as a buffer between the two sets of projections and allowing the motor shaft to turn relative to the worm for a fraction of a revolution to gain inertia and speed helpful to break loose a jammed gear train .