Manufacturer: Leupold 49855
QRW (Quick Release Weaver) mounts use an adjustable double-lever mechanism to lock the rings securely into the base. You simply rotate the levers to achieve a lock. The spring-loaded levers can be "parked" by pulling each lever out, disengaging it from the locking screw. This allows you to adjust the levers to the desired position. Then, just release the levers back into the spring.
QRW rings are engineered to retrofit any existing cross-slot base, thus converting existing mount bases into a quick-detach system.
However, for the kind of fail-safe, return-to-zero performance that's typical of Leupold Detachable Accuracy Mounts, they recommend that your team QRW rings with QRW bases(not included).