I got a couple of pin-lock kegs (for free, so I can't complain.) My problem was when I took every thing apart to sanitize and replace seals/gaskets, I didn't pay attention to which pin-post went where.
When I got my CO2 tank and lines, I wasn't sure which connector fit to which post.
I also learned something else: One of the kegs was made by Cornelious and the other by Firestone. The tubes and pin-posts are NOT interchangeable. For example, one of the beer tubes (the long one) is straight and the other has a bend. The bottoms of the kegs are different to account for the tubes.