How to determine the thread wire size needed - Buttress Thread Gauge



I have a 12 t.p.i. buttress thread plug gauge with a go p.d. of 4.1319'' & a no-go p.d. of 4.23''; can anyone tell me how to determine the thread wire size needed to measure this? And am I correct in thinking the standard should be set at 0, as this should be a measure over wires?
Thanks in advance for any help.


While I can't directly answer your question, I would suggest contacting a major thread gage supplier, particularly one you already do business with. We have personally had success with Swanson Gage and Glastonbury Southern Gage, but there are certainly many more companies out there.

I hope this helps.



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Try this video, which also demonstrates the formula for calculating the wire size needed for a given tpi and how to make the measurement. (It can only be viewed on the Youtube site).

The perfect scenario formula is apparently 0.57735/n = required wire diameter; (n=tpi). I found the video very informative, and had never been exposed to this subject before.
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The three-wire method should work, but anyone doing so should be using buttress thread wires as the "standard" thread wires are only for the "American" thread form. Standard thread wires will say type 60?. There are also different buttress thread forms so you need to know exactly which one you're dealing with. The common buttress thread form in use is 45?/7? but it's not the only one. These three-wire measurements are based on a constant value provided for the measurement over wires. If you have the wrong constants, your measured values will be wrong. I don't personally know how to do the calculation and wouldn't even attempt it. Hence my original recommendation.

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