If you need to drill and tap your rifle or shotgun, you need this fixture! This fixture is designed for drilling almost any receiver between the diameter of .630" to 1.535", in almost any shape be it round, flat or octagon. With hole spacing choices of .500, .605 or .860, you can install almost any scope mount base in the industry! The “scissors” action of the fixture will automatically center itself. The fixture comes complete with one each #31 and #28 hardened steel lock bushings for drilling #31 (6-48) and #28 (8-40) thread sizes. When locked into position, the lock bushings will not spin in the fixture, avoiding scratches around the drilled holes. After #31 holes are drilled, you can use the #28 bushing as a tap guide for 6-48 taps. You will have fewer broken taps and perfectly straight tapped holes. The Williams Scope Mount Drill Fixture is an excellent addition to any gunsmith’s workbench.