I had to file the bottom of the square hole, on mine to get it to lock in. but the filing was minor. I would strongly advise puting blue loctite on all the threaded screws.especually the tinny ones. I went to clean my gun and lost one.but I found it on the kicthen floor.I thought I lost it forever. It was like finding a needle in a hay stack. Any how the blue loctite should help keep them from droping out so easy.and when you shoot a lot the rail tends to loosen up.loctite will stop this. I will say this about the rail,it looks awsome and does something the other rails don't.It fits the gun an