Abstract: A centrifugal clutch comprises a clutch drum and a one piece rotor of resilient material. The rotor has a central hub portion and two like weight portions on diametrically opposite sides of the hub. The weight portions are connected to the hub by integral curved spring portions which are relatively long so as to have a relatively low spring constant. The spring portions are of selected varying widths along their length so as to provide substantially equal fiber stress throughout the length of the spring portions when they flex under the action of centrifugal force on the weight portions to bring them into engagement with the inner surface of the drum and are subjected to driving force transmitted through the spring portions from the hub to the weight portions and hence to the drum.