hese actuators are designed for use in pneumatic control systems to position air control dampers in response to signals from pneumatic controllers. The M556 is a large swivel-mounted actuator with an adjustable crank arm having a clamp to fit a 1/2 in. O.D. damper shaft. 3-12 Spring Range psig, Right-angle, Actuator with ball joint to accept 5/16 in. push rod.