Summary

Print upside-down, like shown in the preview. No supports needed. I strongly advise to print multiple knobs at once to allow for sufficient cooling of the layers.

Made for this specific potentiometer:

https://www.conrad.de/de/leitplastik-potentiometer-mono-50-k-tt-electronics-ab-p160kn-0fc20-b-50-kr-1-st-452798.html

(Or equivalent 6mm shaft potentiometers)

You might want to fiddle around with the settings in the scad file; they are dialled in for my (quite worn out) Kossel printer using Slic3r. It took a few iterations.