A clutch comprises two plates each connected to a respective shaft, so that rotary power may be transmitted. One shaft exerts engagement force near the center of the first plate, whereas the second shaft exerts engagement force about the circumference of the second plate. In this manner it is provided that the first plate tends to deform convexly, whereas the second plate tends to deform concavely, as the plates approach and then engage each other. Due to the geometry resulting from the deformation of the plates, engagement surfaces on the first plate are urged towards receiving surfaces on the second plate, with said surfaces entering into firm contact with each other, as said plates deform convexly and concavely respectively; despite the fact that when the plates are undeformed, there may be clearance rather than interference between said surfaces so that rotation is not transmitted between the plates.