Leupold Mark 4 tactical bases and rings are the strongest of all Leupold mounting systems. The one-piece base features a built-in 15 MOA slope for long range shooting. Both 6-48 shoulder screws and the larger 8-40 screws are included to accommodate high recoil applications. Strong 1/2 in. keeper nuts lock the rings solidly against the one or two-piece bases or any Picatinny-style rail.