A rotor disc for an electrical machine is disclosed. The rotor disc comprises a series of magnetisable members arranged in a circumferential series on a surface thereof and against peripheral retaining structure of the disc. The disc also includes a retainer fixable to the surface and arranged for assisting in retaining the members at least axially on the surface when so fixed. The retainer is arranged to abut at least one of a substantially circumferentially and substantially tangentially extending, radially inner part of each member and thereby to provide the axial retention.