This nice quality unplated No. 6-48 fillister head screw is made for mounting a rib, or rear sight.
This is a popular gunsmithing screw thread size, often used on modern telescope mounts, T/C rifle ribs, most InvestArm rifle ribs, and Lyman Great Plains rifle ribs.
We offer gunsmith quality carbon steel plug taps, bottom taps, tap drills, and clearance drills, for easy installation of this screw, at low cost.