Lee ultimate spline drive lock rings. 3 pack of aluminum lock-rings with o-rings. One wouldn't think you could improve on a simple thing like a lock ring, but we have. The new split clamp spline drive makes all other lock rings obsolete and clumsy to use. We started with custom extrusion of high strength aluminum with a splined exterior surface. We split the ring, and added a cross bolt that when even lightly tightened, applies a vice like grip on your dies. No tiny set screws that easily strip or damage your die threads. Then we added the famous Lee "O" ring because no matter how securely you have the lock ring clamped to the die, it will loosen in the press during Mfg: Lee Precision