Lee started with custom extrusion of high strength aluminum with a splined exterior surface. They 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 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 operation without the friction of the "O" ring. The "O" ring allows you to finger tighten into your press and it will never loosen during operation yet you can easily remove your die with finger pressure. Also included is a handy slim profile lock ring wrench, works great when fitting dies on a turret or tool head. Dies are simply easier to install with the lock ring wrench. Compatible with 7/8 x 14 threaded Lee reloading dies and Lee reloading presses Torque type splined exterior, for a no-slip grip "O" ring, anti-rotation, included. Never loosens during use Lock-ring wrench included