This B2-LR-II Lever-Release Clamp from Really Right Stuff is compatible with most Arca-type camera plates, camera bars, and multi-purpose rails. The jaws of the clamp open wide for plates to be top-loaded quickly and easily.
The locking lever release is opened or closed by only using finger force, and once the clamp is locked down onto the plate, it has a holding power of up to 50 lb. At the top of the clamp it features three counter-sunk sockets. The center socket has female 3/8"-16 threads and it accepts metric 6 and 1/4"-20 threaded screws via a bushing adapter when mounting to a ball head stem. Two additional 1/4"-20 threaded holes are spaced 30mm apart from the center socket.
The CNC machined 6061-T6 aluminum clamp has a black anodized Type II finish. Index marks are laser-engraved on both sides of the clamp so a position can be repeated reliably. The stainless-steel locking-lever has a low profile, and the lever hugs the side of the clamp very closely, so it is very unlikely to snag onto clothing or something else in the field. The clamp has a built-in bull's-eye spirit level, which keeps your camera leveled in a horizontal plane.