The standard 8.5" double socket arm has a socket at either end to allow a 2.25" diameter ball accessory to be connected. A tightening screw on the side of the arm enables the sockets to clamp firmly to a RAM 2.25" diameter ball. When loosening the side screw, a single spring inside the arm opens the sockets allowing you to pivot the ball and socket connection or completely disconnect the ball from the socket.