An electromagnetic actuator has a U-shaped yoke with substantially parallel legs and a keeper which is pivotally mounted for angular movement about an axis located outside of the yoke to move between two angular positions bridging the yoke legs. The proximal end of the keeper adjacent the pivot has a side face which confronts the end of one pole leg forming a variable length gap called the proximal gap, and, the distal end of the keeper has an end face which confronts a side pole face of the other leg of the yoke forming a gap, called a distal gap, the length of which changes very little between and in the two angular positions of the keeper. The torque constant over the displacement range between the two angular positions of the keeper only slightly changes. The design permits keeper movement through a large angle while minimizing operational current requirements.