Specifically designed for use with Leupold's line of STD one- and two-piece mounting bases, Leupold Standard STD 30mm rings are available in four different heights (low, medium, high, and super high). With this many options, you can choose the right extension rings for you and your scope. STD rings are precision engineered to match up with STD 1-piece or STD 2-piece bases Rear ring is secured by windage adjustment screws. Available iin 30mm in four different ring heights Machined steel construction