I think I used a 1/4 drill bit - started by seeing what would go thru and them took the first one that didn't go thru and used it to drill- took about 2 seconds to drill out- worked fine.Has anybody drilled out their sub 2k rear sight to a larger diameter? I will ream it to get a cleaner hole. If so, what dia? Or should I not do it. Hard to pick up with such a small hole.