An electro magnetic device comprises a pair of relatively movable magnetizable members which have surfaces disposed in face to face relationship. One of the members is provided with spaced projections which locate in spaced slots formed in the other member, the projections having a smaller width than the slots so as to permit limited relative movement between the members. Some or all of the slots accommodate an electrical winding, the connection of the winding or windings being such that any two slots in which the flow of current in the windings therein is in the same direction are separated by a slot with either no winding or with a winding in which the flow of current is in the opposite direction. When the winding or windings are energized and when the projections are not centrally disposed in the slots, the members will be urged relative to each other to reduce the size of the smaller gap between each projection and the side face of the associated slot.