Easy to print GoPro ball joint mount. Instead of actually ball (which is hard to print), it uses a sandwich of several parts bolted together:
1) Top mount with GoPro pins, a hole, and a sphere
2) Middle part with outer/inner spheres and a wide hole in the middle
3) A sphere with an m4 hole
4) Bottom GoPro mount bracket.
Additionally, you will need an m4 knob of your liking.
1 and 3 bolted together using an m4 bolt+nut or screw with two nuts. When you tighten this bolt 1 and 3 jams part #2. Part #4 bolted to #2 using two m4 screws. It holds quite well and does not wear, easy to print and easy to use. The weakest (or wobbliest) part is the 2-4 link. It works well but not rock solid.