The NcSTAR 30mm Cantilever Ring Mount/Weaver Style is constructed of hard anodized aluminum for maximum stability of your optic sight. It extends your optical eye relief forward creating more clearance and versatility. It works perfectly with 30mm optic sights or 1" optic sights using the included inserts. It perfect height for co-witnessing your reflex sight with your BUIS. It secures easily with the slotted thumb nut to virtually any picatinny or weaver style rails.