This tool cuts space for the sight screw head, allowing it to be countersunk into the metal. Counterboring a receiver or barrel for sight screws results in a professional looking installation that will add beauty and value to your gun. Notes:Cuts space for sight screw head (allows head to be countersunk into metal)Should be used in a drill press with all work held in precision fixtures for best resultsDescription lists either hight speed steel or carbide. Carbide will last longer than high speed steel, however both must be used carefully as with any cutting tool.