I used the tuners for the Libre Travel Uke https://www.printables.com/model/384349-libre-travel-uke but they didn't fit, so I made them thiner and shorter. The new post size is 7.5mm of diameter and 24mm tall (just for the thin part).

This post is thinner, hence it is much weaker. I suggest to print it in horizontal orientation with supports for higher resistance.