Printables has quite a lot of good and useful "center finders", but I could not find one that I like, so I as a good maker, I decided to “re-invent the wheel” yet again.

This Center Finder is a scissor like which adapt to many different diameters and can be folded to be stored taking little space.

If you wanna tinker yourself and upgrade the model, please take a look a the project on TinkerCAD: https://www.tinkercad.com/things/67dZiXYtNPS-center-finder. I kept some fitting test objects there as well.

PS:  When printing the Nut, if it gets too tight, try scale it up on both X and Y axis just a tiny bit. I would not encourage scaling it up on Z axis as the thread may not fit at all.