I've always kind of guessed at how to size a circular hole/socket for a circular post.
Many times it works, often it requires a model change and reprint to get it right.

I thought I would create some test objects to get a little more knowledgeable on the matter.

These are sets of holes and posts to test how your slicer and printer combine to create objects that slide or even snap together.

The test pairs are for 2, 4, 8, and 16 mm holes and posts.
The middle post or hole is at the exact dimension and the ones above are bigger and the ones below are smaller.
The diameter change up or down for each step is noted in the print.

I found that the 4mm posts were really weak and broke relatively easily on standard slicer setting of 2 walls # 0.2mm layer height.

I included a 4mm post version which are actually tubes with an inner dimension such that exactly 4 wall layers are printed when using 2 walls slicer settings. they are MUCH stronger. (this assumes a 0.4mm nozzle)

You could get the same effect by changing the slicer to use 4 walls, which is OK for this test but might not be what you want to do for an entire print of an object with posts of this size. YMMV.

Many of the posts wind up a little wider at the top probably due to the top surface being printed too. This is very easy to file away with a small needle file. Putting a small chamfer on the top of the post with the needle file also helps them fit.

My general results:

2mm:
Generally the posts come out irregular and I could only get the smallest (1.7mm) to fit into the largest hole (2.3mm) with some light filing. This is size regime is not really useful for my printer in PLA.

4mm:
Generally the post had to be 0.3-0.4mm smaller (with light filing) to fit nicely with a chance of extracting. The next size smaller posts would fit (usually) if pushed hard but good luck getting them out or not breaking the post.

8mm:
when not filed, posts 0.1-0.2mm smaller would fit in.
Lightly filed/chamfered posts 0-0.1mm would fit in

16mm:
Not filed posts 0.2mm smaller would fit well or pretty tightly.
Filed and chamferd posts the same size as the holes worked well for me.