Thanks to my knowledge gained in practice I know that this product is not worth the investment .The coupler failed on the first use causing endless headaches for my travel plans. the pros? None. The cons? Everything. Avoid this product at all costs..
Pros
Durable and strong construction can withstand tough weather conditions and resist tampering.
Cons
Requires a key to unlock, which could be inconvenient if the key is lost or misplaced.
I have just purchased two of these Master Lock hitches from Revain and they are both good and work as intended! If I need another one I will definitely come here and buy another one. I don't think the dimensions are listed, but this coupler fits 3" ducts.