I needed an adjustable mount for some motion sensors. There's a recessed hole at the bottom of the base so that you can screw it to a wall. Then the ball goes in. Next the clamp piece. I made two versions. One without knurls one with. Mix and match to your preference. I've found that having either the clamp or base knurled is good enough to get a good grip for tightening. For the best grip use both knurled parts. For the cleanest look use the plain parts.

I printed these at .2 and .3 layer heights. Both seem to work with .2 having a bit smoother operation.

The mounting holes have 4mm diameter.

The .amf files are what I used, but I added the .stl files so you could get a 3d view on Thingiverse if you want it.

Some pictures show the motion sensor holder attached, but that isn't a part of this thing.

This was designed completely in FreeCAD.
It was a pain to learn it, but I really hate the subscription/cloud model of Fusion even if it is free. FreeCAD is open source and getting better all the time.