ok got cha, what you are refering to is the hitch and reciever set up, for small things like atv trailers theres only going to be one kind, and its available at any welding shop or u haul, hell even wallmart sells hitches and recievers. if you step up to some of the bigger equipment then some use a gi hitch, whitch is like a "hook" but you will not find a small trailer with a gi loop on it unless it was a special made deal. ill dig up some pics and show you a standard 2 inch hitch and ill take a few pics of all my recievers and explain the differences, if no one beats me to it. if you dont mind me asking, why do you ask and are you planing on getting a hitch installed on your ride ?