Overrunning clutches transmit torques in one direction only. They are often used for reversing operations, in order to prevent loading by rotating masses. As a rule, pivoting, spring-loaded keys engage grooves. The flanks of these grooves are designed in such a way that driving by the locking keys is only possible in one direction.
Preferred applications include rotary mowers and flywheel drives, often in the form of a combined friction and overrunning clutch.