Scope rings clamp the scope tube to your base or rail — get the diameter and height right and the rest is torque. Tube sizes run 1 in, 30mm, and 34mm; heights from low (small objectives, bolt guns) to extra-high (big objectives, AR-height stocks). Shop Leupold, Vortex, Warne, Burris, Talley, and Seekins in steel and aluminum, for Picatinny, Weaver, and proprietary bases.