The use of needle bearings and the hardened bearing surfaces make the clutch engagement extremely easy. This is also assisted by the finer teeth of the clutch and the increased length of the coupling attachment. Its suitability for high shaft speeds, especially when these are maintained for long periods, is a further advantage of the needle bearing. An oil-hole is provided in the clutch mechanism to accept lubrication. In the completely assembled safety clutch handwheel, there is a lubrication fitting located in the hub of the handwheel to lubricate the safety clutch unit.