Multipurpose ball joint system that fit all my needs. Very handy !
The ball diameter is 17 mm.
Clean the edge of the inner sphere prior to assemble (gently !)
I joined a bunch of parts that I use, but some of them are probably too specific of my needs.
(Here is a probe holder that use this ball join system https://www.thingiverse.com/thing:2622171
Edit 04/05/2019 : Added 2 easy to print sets. One set have thru hole inside to allow the passage of wires. "Ball join 1st.stl" have holes inside and on the side for entry and exit of wires.