Ruskin model RUS-S24(S) electric On/Off spring return actuator designed for factory mounting on damper up to 6 sq. ft. with blade and jamb seals. Actuators can be mounted directly to a damper shaft from 1/4 to 1/2 inch (6 to 12 mm) diameter with a universal clamp. An optional line voltage auxiliary switch indicates an end-stop position or performs switching functions within the selected rotation range.