These rings are machined from solid steel, they 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) Mark 4 Bases Accept (mark 4) Mark 4 Base Availablilty (Mark 4)