This is a 2" bar mount that utilizes one of the standard GoPro bar clamp screws and a hinge.

The hinge point is 3mm and I used a short section of 3mm threaded rod; however, the CAD files are attached, so this aspect may be changed to fit your style.

The photos don't show the acorn nut recess for the camera mount; however, this feature has been added to the current STL and Thing files.

Enjoy.