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How to use a NPT (National Pipe Taper) thread gauge?

Using NPT thread gauge is actually pretty simple if the Go thread plug gauge for NPS goes into the threaded tear and no-go doesn’t then the application is normally considered within acceptance limits and tolerance. Utilizing National Pipe Taper thread gauge (or ANPT thread, NPTF thread) can also be smooth since you just have one main L one gauge that acts as both go/no-go using the gauge ring or notch face to line up with end of the application thread +/_ allowance tolerance the vital thread shape is within compliance.

Of course, with ANPT and NPFT the complexity boost when the L2-L3 is called to examine compliance to a wrench tight spot and thread taper.

NPT Thread Gauge Facts

Working ring or working plug is exactly that, a thread gauges utilized to check your applications; it’s not setting plug, master ring or master plug. Those are utilized to test the NP formwork plugs and rings to ensure they’re in compliance.

Which end of the NPT, ANPT and NPTF thread Ring is up?

So I hate to admit but actually, this comes up occasionally. Of course, the BIG end is facing the application which is normally obvious. But the real question being asked is which last point of the thread ring gauge is marked. ASME specifically in part B 1.20.5 for NPTF thread that the ring is marked on the face of the huge end. B1.20.2 for NPT thread gauge doesn’t make that distinction but, and this possibly a place where we utilize the world Assume which everyone knows can get us in problem, almost all thread gauge OEMs will carry the NPTF convention over the NPTF thread gauges.

I must be careful here because there’ll always be exceptions that find the marking on the backside or both sides or if specified by the customer on the small end side. Because ASME B1 .20.1 doesn’t need this marking convention now, you might find variations so when in doubt look at the measure or gauge the minor ID if you can that hopefully will give a clue as to which side is small and which side is big.

NPT thread gauge/NPTF differences

These are due to the fact that NPTF is utilized as a dry seal while NPT thread Gauge needs some kind of sealing medium to prevent leaks.

With NP threads gauge, both straight and tapered, for fuel and oil as described in B1.20.5 and 1.20.3. Conformance to the L1 to L3 feature might not be sufficient to assure that the threads will dry seal.

In addition to the usual feature inspection these gauges give you need to ensure to thread root and crest truncations are held on all mating applications. The plain six-step ring or plug can be utilized to confirm that the thread crest is with limitations. In class two threads the L2 to L3 as well as six-step crest inspection is needed.

NPTF might also need L1-L2 in basic or in three-step and or four-step configuration, based on the needs placed by the user for the checks performed. As we recommend, you’ll definitely need to have to replicate of ASME B1.20.5 & 1.20.3 on hand to reference for NPT gage requirements.

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John Winer

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