Abstract: An electrical contact brush having interposed in a central longitudinal slot an abrasive element which frictionally contacts the commutator surface at crests where the radius of curvature of the commutator is less than that of a concave contact surface preformed at the distal end of the brush but which does not contact the commutator at valleys where the radius of curvature of the commutator is greater than that of the brush contact surface, said element in operation mechanically reducing the average radius of the commutator at a rate faster than the rate at which the commutator surface is electrically eroded, thereby tending to maintain a true cylindrical commutator surface with uniform wear characteristics.