Npt threads for the pros.

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ImpactX

ImpactX

Member
May 4, 2019
636
19
Minnesota, United States
Anyone know about npt threads? I thought npt are standard and only 1 type. I purchase one 1/8 male npt and one 1/8 female npt from 2 different sellers. They both said threads are npt. When I got them, they will only screw in 2 turns and get hard and won't turn by hand anymore. Even with a wrench it will barely turn 3 before it feel like I might damage the threads. So why would 2 npt fittings not fit? Are npt thread not standard and there are many type or what? On the male I can see it is tapered. But on the female I can't really tell but it looks like its parallels. Isnt npt tapered and not parallels? Seller lied or what. Did I get 1 fitting in bsp/m10? Damn wasted money on fittings that doesn't fit.

This is how far it will screw in. 

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If the female thread looks parallel then it is probably BSPT and not NPT. BSPT is a British and Australian pipe thread type, I believe. Plus, sometimes Imperial thread sizes are cut by manufacturers using metric machinery, and they just get it "close enough." It sucks that these manufacturers can't seem to get on the same sheet of music sometimes.

James
 
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If the female thread looks parallel then it is probably BSPT and not NPT. BSPT is a British and Australian pipe thread type, I believe. Plus, sometimes Imperial thread sizes are cut by manufacturers using metric machinery, and they just get it "close enough." It sucks that these manufacturers can't seem to get on the same sheet of music sometimes.

James
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The male side i can easily tell its tapered so looks npt. But the female side is just a hole with threads to hard to tell but it looks parallels. But on the listing it says 1/8 npt. I asked seller and he said it will fit any npt threads. But when received it, it doesnt screw in. Its about 7 bucks so not worth the trouble returning it. I just order another from a different seller. Was confuse if there are many types of npt threads and both fittings are npt but just different type thats why it doesnt fit. Is there any way to tell if our fittings are npt, bsp, m10? They all look the same to me with the naked eye.
 
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Do you have a spare gauge for your PCP laying around. Most of those are BSPP. At least you could see how it might screw into your new fitting.jking
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Yes i have some old fx guage I replaced with wika. Didn't even think to try using guages to test. I tried the fx gauges and screw easily into it and bottom out. So this female 1/8 fitting isn't npt. So seller either don't know what the heck he is selling. His posted stated its npt thread. Cant believe some seller don't even know what they are selling. Smh. When it didn't fit I thought there are many type of npt thats why. Now I know its not npt. 

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Female npt threads look tapered. M10 is close but not a match. 1/8 npt is 27 threads per inch. British tapered pipe threads are 28. Look close but not the same. Buy from a reputable source, good catch in not just letting it slide. You need 4-5 threads of engagement to handle pressure, or whatever the spec is, cant remember.
 
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True NPT threads are tapered and after the first couple threads need a wrench to turn to connect them. The idea is that the taper creates a seal as the threads are tightened. There is also a NPSM thread which is straight and not tapered. Sometimes the SM is used in conjunctuon with the tapered so more threads can connect when a seal is not the predominate requirement. Buying online or not buying from a reputable supplier can cause these mixups. When talking extreme high pressure connections, this is not the time to cut corners to save a few bucks. You need to be sure you have true NPT matching threads..
 
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IF I buy fittings for anything relating to 4500 psi air guns I go to Mr Brancato. My dad demonstrated what 300psi air leak could do. It cut all the straw strands off a broom. It was the technique they used to find leaks in a noisy utility tunnel. To walking slowly and waving a broom from ceiling to floor. I found out that 300 psi is sufficient to cut or remove some body parts. An air injection as you know can easily be deadly. As an electrician I found that 3/8 nuts and bolts from the same chinese manufacturer did not even start to thread together. I had to use a 3/8 tap in a battery drill in the nuts to have enough for the job. CHEAP BOSS buying cheap chinese junk. I know I will be moving around the fill set up as I fill my guns. I use a piece of notebook paper to check for leaks often and quality fittings. The least that can happen with a leak is a cut any injury beyond that will be memorable. please reconsider the value of everything from your sight, to your well, being to your life. The less fittings you have in your system the better.
 
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