During normal running torque is continuously transmitted from the hub to the flange through balls or rollers held in indentations in matching halves of a carrier flange by disc springs. As the torque exceeds a pre-set limit the balls or rollers are forced out of their indentations, allowing the flange sections to rotate separately. At this point the torque being transmitted is negligible and a limit switch is activated to signal emergency stop of the motor. In Quick Guard versions re-engagement is automatic as soon as the torque has fallen below the pre-set value. Synchronous versions also re-engage automatically but after one full revolution has been completed. In the Continuous version, the rollers are prevented from fully disengaging and a switch is activated to signal motor stop. The Free Running version also disengages the drive at a pre-set torque value but must be manually re-set to re-engage the drive.