A stator for an electric motor, the stator comprising a back-iron having a first surface and a heat sink having a second surface, wherein the first surface of the back-iron includes a plurality of keying features arranged to retain the heat sink to the back-iron, wherein the heat sink is arranged to provide cooling to the back-iron via the second surface, and wherein the second surface has complementary keying features to the plurality of keying features on the first surface that are formed by casting the heat sink on the first surface of the back-iron.