Sometimes you need to clamp a GoPro to something, but you can't use a clamp that goes all the way around the something. This mount is for that.
You also need two pieces of metal hardware for this (pictured): an eye screw, and a barrel nut (sometimes called a dowel nut). I got both from the local Home Depot, hardware aisle. The eye screw was 4"x1/4"-20 and the barrel nut was threaded for 1/4"-20, and was 10mm in diameter.
I recommend printing the clamp mount with like 2mm wall thickness, and maybe 50% infill. The pusher stop (a little plastic cylinder that the the eye screw will push against) you must print at 100% infill. This piece may wear out over time; but that's ok, because you own the factory that makes them.
You can print this thing in-place. The two clamp arms will be permanently hinged together.
It requires a little bit of support, but not much. When you're done, insert the pusher-stop into its hole, and insert your barrel nut into its hole, and screw the eye screw through the barrel nut, and voila. If your clamp arms don't move freely upon printing, use the eye screw to tighten the clamp, and the arms should break free.
I glued pieces of old bike inner tube on the insides of my clamp arms, for better grip.
You can customize things with the OpenSCAD file. Note that it requires Mooncactus' excellent GoPro scad file (https://www.thingiverse.com/thing:62800).