4mm stick

Lots of multi-piece 3D prints require you to have a rod, shaft, or anything else that is basically just a stick to use.
If you, like me, don't have a microscopic "rod" laying around, then you can just use this (or one of my slimmer or thicker models) to make up for it.
Isn't the length you're looking for? Try trimming it shorter or making multiple to use both. It only takes twenty minutes to print, after all!
If 4mm isn't what you're looking for, check out my account for other options:
https://www.thingiverse.com/kingbob472179/designs