This variant of the CAT 12 V plugs & sockets is intended (a) to lock together so they can't vibrate apart with motion and vibration and (b) the plug is hooded so touching it against metal can't accidentally short circuit it. This is useful for example with a battery and a battery charger where both sides of the connection can be live. A regular CAT plug can plug int a click-lock socket, but a click-lock plug can only plug into a click0lock socket. A click-lock socket can be mounted in a wall plate but will stick out instead of being flush. (As produced on my printer they don't really "lock", but they won't vibrate apart with typical vehicle motion, either. This can doubtless be adjusted if necessary.) See all CAT Standard plastic connector designs on Thingiverse.com . See all usage & wiring techniques in www.TurquoiseEnergy.com newsletters.