not very mechanical and new to bikes. Bought a Bor Yeuh rack and it doesn't have instructions. I've finally figured out where most of the nuts and screws go but am missing a few. My bike frame has a couple of metal studs that look like they can be removed with an allen wrench. Are these meant to be removed and replaced with mounting screws for an accessory? If so, anybody know the typical size so I can pick up the missing parts for my rack?