Machined from solid steel, Leupold Mark 4 30mm Rings Matte Finish Super High (8-40 Screw Adaptable) offer superior integrity and tighter tolerances that are based on the proven cross-slot design. Use Leupold PRW bases or any other Picatinny-style mount rails. Mark 4 CQ/T A.R.M.S. Throw Lever Mount Leupold Mark 4 CQ/T Flat Top Mounting Bracket Leupold Mark 4 AR-15/M16 Handle Mount Slot and Spline Design (Mark 4) 8-40 Adaptable (Mark 4) Large caliber rifles are becoming more and more popular with today’s shooters. Mounting large riflescopes on these firearms with conventional 6-48 screws is not ideal, as the increased recoil and scope weight can over stress screws and lead to possible failures. New, more rugged, 8-40 screws increase mount strength by 41%, and are fast becoming necessary equipment on larger caliber rifles. Leupold is proud to announce the first mount that can accommodate both the oversized 8-40 screw and a conventional 6-48 screw. This mounting system features larger through holes that accept the thicker 8-40 screw, and the standard 6-48 screw has been replaced by a shoulder screw to work with the larger opening. This will give you the flexibility to mount your rifle with the common 6-48 screw size, or drill and tap your gun to accept the 8-40 screws. ADAPTABLE MOUNT FEATURES: Will accept 6-48 shoulder screws and new 8-40 screws. Both 6-48 shoulder screws and 8-40 screws are included (6-48 shoulder screws are stronger than standard 6-48 screws). 8-40 screws are 41% stronger than standard 6-48 screws.