Electromagnetic clutches

In an electromagnetic clutch which includes a first magnetic rotatable member rotatably supported on first bearing means, said first rotatable member being provided with at least one annular groove in the outer surface thereof for receiving belt means operatively connected to an external power source to be rotated by the external power source and having axial end magnetic friction surfaces, a second rotatable member rotatably supported on second bearing means, an annular magnetic member being supported on said second rotatable member so as to be capable of limited axial movement and having an axial end surface which faces said magnetic friction surfaces of said first magnetic rotatable member with an axial gap therebetween, and electromagnetic means associated with one of said first rotatable member and said annular magnetic member for attracting the other member, the improvement comprising said first rotatable member having an annular body of magnetic material, a pulley member having said belt-receiving groove in the outer surface thereof which is formed of aluminum alloy, said pulley member being disposed on the outer surface of said annular magnetic body by casting, said annular magnetic body having an outer annular portion and an inner annular ring, an axial end annular plate portion integral with said outer annular portion and joining said outer annular portion and said inner annular ring at an axial end thereof to define an annular hollow portion, said electromagnetic means being fixedly disposed in said annular hollow portion, said inner annular ring being joined to said axial end annular plate portion at the radial inner end, said axial end annular plate portion having said axial end magnetic friction surfaces, said axial end annular plate portion having an annular axial boss at the radial inner end thereof, said annular axial boss including an axially projecting end, said annular axial boss being fitted into and fixed to said inner annular ring, and said axially projecting end of said annular axial boss serving as a stopper for preventing axial movement of said first bearing means.