A useful part for "Articulating Raspberry Pi Camera Mount for Prusa MK3 and MK2" by Sneaks. Sneaks's nut and bolt work fine, but when assembled, they look identical. Both are knurled, so when assembled, you can't tell which rotates and which is fixed.

This nut has a smooth surface, so you can easily tell which one turns and which never turns.

This way, when you disassemble or adjust, you will know which part to turn.

Here is the original: https://www.thingiverse.com/thing:3114849#Summary

I brought Sneaks's original part into Fusion 360 and removed the knurled surface.