Abstract: One face of a coupling disc (i.e., the armature or rotor) of an electromagnetic coupling such as a clutch or brake is formed with a plurality of radially spaced and circumferentially extending grooves. The other face of the disc is formed with a plurality of radially spaced rows of circumferentially extending slots which communicate with the grooves so as to form air gaps completely through the disc. In the preferred embodiment, each groove is circumferentially continuous while each row of slots is defined by circumferentially spaced slots which are separated by short bridges. By virtue of forming the grooves in the disc, only a small thickness of material need be removed from the disc in order to form the slots.