This B2-Duo Sliding Screw-Knob Clamp from Really Right Stuff has mounting surfaces on the top and bottom of the clamp that mount onto camera bars and rails in a parallel orientation. Lens plates and dovetail telephoto lens feet mount the same way, but a camera should utilize a camera bar to position itself in the same manner.
The main locking knob controls both clamps, and the primary clamp holds camera plates, L-brackets, lens plates, and dovetail telephoto lens feet. At the same time, the secondary clamp holds onto camera bars and multi-purpose rails. Besides the main locking knob, there are two thumb screws that also work independent from the main screw-locking knob and lock the second clamp. Having this feature also allows the clamp to move up or down on a camera bar or multi-purpose rail, which is a very useful feature for macro photography or as a nodal slider for a telephoto lens.
The B2-Duo Sliding Screw-Knob Clamp accommodates only Really Right Stuff or Wimberley camera plates, lens plates, multi-purpose rails, and camera bars, because the main locking knob controls both jaws at the same time, and the accessories have to be the same external dimensions in order to fit. The CNC machined 6061-T6 aluminum dual clamp has a Type II black anodized finish. Index marks are laser-engraved on both sides of the clamp so a position can be repeated.