On the side of the AL-KO 2" coupler on my Cobra trailer there is a "keyhole" shaped hole. What is it for? It sure looks like some type of locking mechanism but no one seems to know what it is for. The coupler is marked "CL4 2" AL-KO Elkhart, IN). I contacted AL-KO in the UK and they directed me to AL-KO in the US but I never got a response.

Thanks, John

Here are some pictures;

https://dl.dropboxusercontent.com/u/...%20coupler.jpg
https://dl.dropboxusercontent.com/u/...%20coupler.jpg