A buddy of mine has a older Trek Pro road bike.The rear wheel fell out while riding we fixed it then noticed there were some small screws in the drop outs ?? Like a BMX except the heads of the screws were in the dropouts not from the rear like a BMX used to tighten there chains.What are these screws for on a road bike .We made sure they were screwed in far enough that the wheel sat in better . I was just wondering. Thanks