Hi, so what the difference is I don't know either. I had trouble with the clutch on the Donkey and it wouldn't fit on any of my bikes (these days bikes have wider frames) and the clutch doesn't seem like it would hold! I bought two different clutches and it still didn't work! There are different couplings and I would inform myself thoroughly otherwise you will be like me, you have a trailer but no compatible coupling to mount this part. I sold mine again. Too bad, it was a total flop and a losing proposition! I bought another trailer where there is no problem with the trailer coupling and it is possible with every bike! Good luck with your trailer purchase!