So I got the pistol grip on my Mossberg 500. I want the swivel stud on there, but it isn't screwing into the hole... it came with two: one is extra small and one is a bit bigger. The extra small one doesn't screw in, period, like you drop it in and the threads don't even seem to line up. The big one works for one screw-in, but then it gets stuck and you can no longer screw it in really. So it's basically sticking out a ton and you can see the threading poking out as well... am I doing something wrong? The manual says "Screw the swivel stud into the left side of the pistol grip". It came with two different swivel studs... this is kinda weird. Please help, thanks.