BURRIS XTREME SIGNATURE MOUNTING RINGS: The XTR Signature Rings were designed for the tactical shooter. They deliver plenty of holding power, with less weight. - Unique, self-centering, dual steel clamps with full cross-through connection assure proper center on any width Picatinny rail while adding extra strength; - Revolutionary Pos-Align Inserts technology, in a tactical ring configuration; - Pos-Align Inserts guarantee perfect centering and maximum scope-to-ring contact for tremendous gripping power without damaging the scope finish; - Lets you virtually sight in your gun without moving the scope adjustments; - Corrects misalignment caused by off-center receiver holes; - Corrects for bases or rings being slightly off-center; - No need for expensive tapered bases or shimming for thousand-yard shooting; - Rugged, robust aluminum tactical rings save weight and mount on any Picatinny and most Weaver-style rails; Each ring set includes one set of the +/- 0 MOA concentric, one set each of the +/-5 MOA and +/-10 MOA, and two sets of the +/-20 MOA. With these inserts, it is possible to make 0, 5, 10, 15, 20, 25, 30, or 40 MOA of cant in the scope.