RS2 is used to limit ETA Shoulder Block rotation, usually to keep arm from colliding with other items in the work environment, like parts bins. RS2 is placed over our base pipe and then the arm is threaded onto the Base Assembly and tightened fully. Then the RS2 is moved up against the Post Cap and its 4 set screws are tightened to the pipe. Finally thread the 2 stops in the holes that stop the arm where desired. RS2 will work with any ETA arm and can be added to your arm at any time.