The B2-FAB 38mm Screw-Knob Clamp from Really Right Stuff is an Arca-type compatible clamp with laser-engraved 1mm scales on each side of 38mm long jaws, so a camera can be aligned within the quick release.
The screw-knob style clamp has anti-twist tabs on the bottom, which fit into recessed channels of compatible rails or plates. Furthermore, plates and rails, without a recessed channel or an open area for the drop-in tabs will not sit flat against the bottom of the clamp. Additionally, a 1/4"-20 threaded female socket enables the clamp to attach to a monopod or tripod without a quick release, and the clamp is constructed using black anodised aluminium.
