A rotor suitable for use in an electric motor or generator. The rotor comprises a hub having a central axis, a plurality of rotor segments and permanent magnets, and an assembly for retaining the segments on the hub. The segments are arranged around the hub to define at least two rings, which are adjacent to each other in the axial direction with a permanent magnet disposed between each of the segments in each ring. The assembly includes a plurality of rods which extend in an axial direction to retain the rotor segments. An intermediate plate is located between each ring of segments through which the rods pass, wherein the intermediate plates and the outer circumferential surface of the hub engage with each other in such a way as to allow the intermediate plates to move axially along the hub.