The screws are small, but you can order more if you break them. Not that I broke any..........
Mine have been on a couple guns from a 20 gauge 870 through an 835 shooting 3.5's. I put a small dab of blue loc-tite on them and I've never had one work loose.
They made a new ghost ring rear that I put on mine that I really like so far so that's another option if you were a fan of ghost rings.