In every AL-KO coupling there is a convenient adjustment screw for keeping the tow-ball correctly tensioned, as couplings do allot of work occasional parts will need servicing after a while and this may include this little tension screw available from AL-KO. How the AL-KO Coupling Ball Screw & Nut works is it provides needed tension to your tow-ball when coupled aiding the couplings tongue to firmly secure against your tow-ball, with ongoing use a small amount of wear can occur and by adjusting this nut you can keep it all connected and ready for more work. A simple part but vital keeping it all together and making your next tow worry free.