Calibration of Thread Plugs and Ring Gages - Various Thread Standards



I send gages out for calibration and we have a form that's called "Calibration Vendor Requirements" that I need to fill out. I thought putting calibrate per manufacturing specs would be good enough but I guess not.

I e-mailed this to my Quality Manager to see if this is acceptable. "On the calibration of Thread Rings and plug gages, per manufacturing specs is based off of what the Gage labeled size is. I believe they follow ANSI and that is what they calibrate to. So for thread gages, could I say all thread gauges will be calibrated to ANSI standards on the "Calibration Vendor Requirements form"?

He replied. 'Not all threads are ANSI, but I think your point is correct.
You may reference the thread standard of the specific thread type.
This does get sticky however because of revision levels change. So ideally you would name the spec and current rev, however, in most cases you will not know and would be relying on the cal supplier to be up to date. So in this case you should be able to say the spec name and “latest revision” or “current edition” etc.

We have UNC, ACME, NPT threads. Can someone help me understand what standard is used that threads are calibrated to? Or clarify what my quality manager is looking for?

Wayne Miller


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Re: Thread plugs and ring gages.

If I understand your question correctly, could you do the following:

For each specific gage, does your system allow you to make a description of the item. For example, part of a description of "9/16-18 UNF 2A" could you add "Calibrate to XXXXX, latest revision"? This would allow you to specify each calibration requirement specific to a gage and if you state, to latest revision, this may allow you to forego specifying a revision level.

Could you use a ISO 17025 lab (I think that is the correct ISO number for calibration). They should be able to help direct the PO and specific requirements.


Re: Thread plugs and ring gages.

I fill out the list of gages that I will be sending.
ID# what it is. And its interval.
I send list to calibrating company and they schedule a pickup. So. I have about twenty thread or ring gages that are either UNC, ACME, NPT. So I'm a little confused when you wrote calibrate to XXXX, Revision? All of the gages have been sent out a few time and calibrated before. It just this new form I have to put something in there so there happy.


There are hundreds of thread standards, if not more. However, the types that you listed (UNC, ACME, NPT) are ANSI standards. One sentence that could meet your quality requirements while remaining easy to handle could be: "Calibrate to latest applicable ANSI standard, unless otherwise noted".

As a cal lab, most of the time this works for us. We use the nomenclature on the gage and pull the tolerances from that. The only place it gets confusing is custom gages (ex: a 15.5 TPI gage, yes they exist) or metric gages. The ISO nomenclature and the ANSI nomenclature is identical, and the tolerances are not.

It all depends on what your gages are and what your requirements are, but from 1000ft, that is my suggestion.
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