Here is the 3rd version of GoPro fixation with Ball joint.
The 1st one is here: www.thingiverse.com/thing:38040
The 2nd is here: www.thingiverse.com/thing:38042
It is made with 6 parts
Think To Nelson for his Help
After a 1st Test I discovered that the complet STL I gave wasn't good.
The position of 2 pinces wasn't good, the structure doesn't resiste when you tight the screw.
I think that the best position is lengthen on the side.
I'll put soon a knew version