A coupler is the connection point mounted on the trailer which connects the trailer to the vehicle. When replacing a coupler there a few things that you have to know. First, what is the hitch ball size for the coupler. Secondly, what type of trailer do you have (Straight Tongue or A-Frame)? Lastly, what is the Gross Trailer Weight of the Trailer. These are the basic questions for finding the correct coupler replacement.