Really Right Stuff Tripod Mounting Plate for Leica R to M Adapter
See previous discussion of the Leica R to Leica M lens adapter.
Also: Camera Plates for Tripod-Mounting Small Cameras (Sony RX100, Nikon Coolpix A and similar).
The Really Right stuff B9-E camera plate is versatile: it works well for the Leica X Vario handgrip, but it turns out that short of a custom design (not yet available), the B9-E also works well on the Leica R-adapter M tripod mount.
The plate is needed to mount the rig onto an Arca Swiss style clamp, which is what nearly all photographers use these days.
Really Right Stuff offers a wide variety of mounting plates and ballheads and tripods using this mounting system. There is no other rational choice for mounting a lens or camera, at least if one wants proven reliability and support for a very wide range of gear.
Shown below is the screw-thread side of the Leica R-adapter M; the B9-E plate screws into that socket. The flange on one side helps prevent any rotation of the plate once screwed on.