This invention describes a method of making a commutator, for a high speed electric machine, (1) embedding a number of conductive bars in insulating plastics material to form a moulded commutator (2) the moulded commutator defining at least one annular seat (3) placing a ring of high tensile material on the seat whereby to stress the ring in tension and thereby apply a radially inward load to each bar which is greater than the centrifugal force on the bar at maximum running speed. The invention also includes a commutator made by this method.