Leupold 51716: The characteristic that distinguishes the Quick Release(TM) system from the Dual Dovetail(TM) and STD systems is the ability to remove the scope from the rifle and reattach it without the loss of zero (within 1/2-MOA). The key is precise machining of the patented lever mechanism on the QR base. Turning the lever forward engages the base of the ring, pulling the ring down and forward, locking it into its \"zero\" position. These rings are for use with Leupold QR bases.