A couple of different 3d printed knob designs. They fit the split/knurled shaft kind of potentiometer - eg Doepfer but very common - turned out every module I tried had these. See photos.

Both are slightly taller than usual euro/synth knobs, so are great for the most used controls. I experimented a bit to get a grippy pattern that still printed ok on my poorly calibrated cheap printer. A freecad file is in there if you want to play with it.

The slim one has a wide skirt for fine adjustments. The big model is the same height but wide all the way up, so is good for sensitive controls. The pointer is a separate part so you can mix and match colours, it should stay in from friction or is easy to glue.

I printed these in a few colours and colour-coded my live rig: filter cutoff knobs are all yellow, resonance orange, etc etc. Makes a world of difference in the dark!