3 special Center Punches with outside diameters (O.D.) that match the clearance drill size of the most popular sight, rib and scope base mounting screws. Ground, parallel-sided punches reach through even the thickest handgun rib. Ends guess-work and hole center-to-center spacing problems. To Use: Level gun in vise or scope mounting jig, position and level sight, rib or base, and clamp in place. Place correct size punch in hole and lightly tap with a 4-oz. hammer. Remove base; drill and tap first hole; re-install base and check positioning. If everything is "square", re-clamp and finish other holes.