Towball setup

[Cascade]

Hi all, I've just got my first Touareg, a 2008 model, and went to install the towball bracket into the towbar but wasn't sure what pin to use as there was two in the bag.
One is just a normal pin with a ring on the end, the other has a lock on the end. I'm guessing they both do the same job but why supply two? I'll try and attach some pictures to make myself clearer.

The first two are the same pin just from both sides of the towbar.