Bolt and Screw

Oh, and a drop of lubricant on the threads too.

Turn in opposite rotation first.

Look for and remove any debris.

Reassemble and tighten.

Plating too thick.

Maybe the plating is not shiny.

First, measure the threads with the proper wires. This gives the basic fit up to the opposite thread.

Judging from your previous posts you may be learning that "All (reverse) engineering (does not provide) doubt clearance"

Poor quality fastening supplier. Buy only from good quality suppliers whose products meet the specifications set in international standards.

Given your questions are you trying to manufacture fastenings yourself or are you just purchasing fastenings from a poor quality supplier?

You might also wish to investigate "Class of fit" for threaded fasteners. There are multiple combinations ranging from "Free running" to "intended interference" and all sorts of combinations in between.

Select thread class based on sound engineerng design criteria!!

You don't state what methods are being used to cut the bolt threads and the nut threads so we can only presume. What is the materials? What size threads? Is it an automatic screw machine? Are the threads being rolled or die cut? What type and size tap is being used to cut the nut threads? Is it under sized? If it is a hand die operation is the small screw on the side of the die tight enough? If not it won't cut enough material off and the mating bolt and nut will be tight. Is it stainless steel? The least bit of dirt or junk on properly sized threads will cause it to gall. Also some lubricant might help.

If you want a good answer applicable to your situation you must provide more and good information. The answer is only as good as the question!

Good Luck, Old Salt

I believe that one of the methods being used is a dull plating of the threads.