The true effect of the thickness of a coating layer (plating or painting) on fastener is much larger than most people think.
Take a M6-6g bolt (1mm pitch) and a M6-6H nut (1mm pitch) for example.
Will they still fit if a 5 micron zinc plaing is put on both of them?
Let us check ISO 965-1 on tolerance and deviation of 6g/6H first.
|Grade 6 Tolerance||Fundamental Deviation|
|Minor diameter of internal thread||236 micron||H:+0 micron|
|Major diameter of external thread||180 micron||g:-26 micron|
According to the table, when a bolt and a nut are made at maximum material condition, the gap between the threads will be 26 micron.
It sounds much larger than a 5 micron thick zinc layer, however, it might cause bad interference.
There are two factors to make a superposition.
Firstly, not going to threads yet, consider a cylinder rod and a hole situation.
When a rod is "wrapped" by a 5 micron layer, the diameter actually increases by 10 micron, and this applies to hole features, too.
In the other word, a 5 micron layer on them will take out 20 microns gap between a rod and a hole.
Secondly, there is additional factor for thread features.
The 5 micron layer on 60 degree thread will actually leads to a 10 micron effect in radial direction by the following calculation:
(5/cos60 = 10)
With superposition of the factors above, 5 micron layers will take out 40 micron clearance between inner thread and outer thread.
Going back to the initial question, a brief answer that Sun Through can provide here is:
it depends on the tolerance left by the maker for fitting, but they will interfere if the fasteners are made in maximum material condition.