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topic 1166

Plating Specifications of Internally Threaded Fasteners


We have some specially designed collar screws made out of 12-L-14 steel that are internally threaded. (10-32 and M-4).We received them in a unplated condition and then have a zinc plate and yellow chromate finish (.0002" thickness) applied. How do I properly specify the internal thread to allow for the plating thickness and how do I check the internal thread of these parts in the unplated condition? Should the screw machine manufacturer use a H-4 or a H-7 tolerance tap on the 10-32 internal threads?

Thanks for your help,

Allan W [last name deleted for privacy by Editor]
-furniture hardware


I believe that I would start by seeing what gage fits the mating screw part. Do you have a system for incoming screws?

When you are confident that your mating screw is under control, I would see how they fit the internal thread of the collar screw, both before and after plating.

You should be able to find some combination which gives you the fit that you want. Then you can set up the acceptance criteria for the collar.

You may find that your incoming mating parts need as much help as the collars.

pooky tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania



Most plating solutions will not plate an ID more than one diameter deep. When you put threads with their high current density areas on each thread it makes it even more difficult. This is very obvious if you have them color chromated and have a small bright light.

You will go thru many platers until you find one that has considerable experience with this type of fastener and has learned how to cheat the system.

It is further a pain because it is a small blind hole, so will retain solution even with excessive rinsing.

In short, a nasty part to economically plate in bulk.

James Watts
- Navarre, Florida

Ed. note: The following letters seem to offer insight into thread allowances for plated parts: 2906, 22409, 31694.

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