I sent this in a PM as well. It shouldn't degrade the integrity of the metal tube if you enlarged the hole a little bit by accident. Where are you located? If you're close to Seattle, WA I could help in person.

I'm assuming that you have loosened the bolt on the strap clamp that is to the right of the pin. The pin is harden and free spinning. So if you don't put enough pressure on it, it will just spin with the drill bit. You have to put a bit more pressure than you would if you were drilling into wood. After drilling for a little bit, grab the assembly and try turning it downwards. the key hole towards the floor. If it turns then it's enough drilling. If not drill a bit more and try turning the whole assembly again.