Ball joint leveling feet (M5) / tilting adjustable foot

A leveling foot with a ball joint to tilt the base of the foot on sloped or uneven surfaces.
Four of these and a 20x100cm plywood sheet let me put plants upright on a 5° slanted outside windowsill.

The ball has a M5 thread, so that you can mount a bolt of your choice. 3D printing does not cope well with small threads (at least for me), so I recommend to finish the thread with a tap.

The bottom part consists of two models – the socket for the ball and a washer. The washer should be printed with a rubber-ish filament like TPU, so that it provides sufficient friction.

The uploaded openscad source file is parametrized, so you can change ball size / thread diameter / looses etc.

Filament:
I used PET-G for ball & socket, but any filament should work. Consider temperature and UV resistance of the filament if you plan to copy my idea of leveling a windowsill. (Probably ASA would be better.)
Washer should go with TPU or other flexible to increase friction and prevent sliding down.

Print settings:
0.2mm layer and 0.5mm nozzle works fine. No supports needed. 

Post-printing:
Check if the ball thread is not too tight, if it is, then tap it first. 
Fasten the bolt of choice to the ball.
Press the washer in the socket and snap the socket on the ball.

For modelling the metric thread, I used the following library:
https://dkprojects.net/openscad-threads/