Abstract: A coupling for two co-axial torque transmitting shafts having the features of a splined torque transmitting joint (5, 6), a screwed joint (9, 10) for effecting axial engagement of the splined joint, interference members (15, 16) axially movable to a locked position in which unscrewing of the screwed joint is prevented, and a detent (32, 33) for preventing axial movement of the interference members from the locked position, the whole being housed in a readily hand grippable housing 19, hand movement of which effects sequential operation of all the features.