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Old 02-08-2016, 08:11 PM   #1
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Default PT vs NPT

I have an oil pressure sensor and an oil temp sensor from a company that specifies that both of these sensors are 1/8-PT/BPT/BSPT/whatever you want to call it. Many people on the internet that actually have these same sensors from the same company have said that the pressure sensor is PT but the temp sensor is NPT. Asking the company to confirm has been useless.

Does anyone here know how to tell the difference between them visibly? Both of these things thread into a 1/8PT hole just fine, but the one that i THINK is NPT has a taper that is visibly more pronounced than the other one.

Strangely I havn't been able to find anything definitive on the internet. Will an NPT sensor threaded into a PT hole not seal well? I don't really remember needing any sealant at all to make NPT seal, and I don't think I've ever dealt with PT before. EDIT: doesn't the oil pressure sender on a BP have 1/8PT threads?

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Old 02-08-2016, 08:22 PM   #2
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Originally Posted by MartinezA92 View Post
I have an oil pressure sensor and an oil temp sensor from a company that specifies that both of these sensors are 1/8-PT/BPT/BSPT/whatever you want to call it. Many people on the internet that actually have these same sensors from the same company have said that the pressure sensor is PT but the temp sensor is NPT. Asking the company to confirm has been useless.

Does anyone here know how to tell the difference between them visibly? Both of these things thread into a 1/8PT hole just fine, but the one that i THINK is NPT has a taper that is visibly more pronounced than the other one.

Strangely I havn't been able to find anything definitive on the internet. Will an NPT sensor threaded into a PT hole not seal well? I don't really remember needing any sealant at all to make NPT seal.

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The difference between NPT, BSPP and BSPT seals

https://www.valvesonline.com.au/refe...ences/threads/
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Old 02-08-2016, 08:36 PM   #3
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The oil galley take-off port on a BP is BSPT.
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Old 02-08-2016, 08:58 PM   #4
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So the threads are sort of smaller on one versus the other from what I've gathered in that link, but my eyes are not good enough to tell the difference lol.
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Old 02-08-2016, 09:09 PM   #5
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It's the angle of the thread taper that is different. That means rather than getting an interference seal over a large number of threads, you only get a seal on one or two . . . doesn't quite cut it.
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Old 02-08-2016, 09:24 PM   #6
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so NPT does have a more pronounced taper.

there should be a "dumb questions that don't deserve their own thread" thread in here lol.
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Old 02-08-2016, 09:36 PM   #7
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so NPT does have a more pronounced taper.

there should be a "dumb questions that don't deserve their own thread" thread in here lol.
Correct.

The NPT will 'thread in' but long term likely will loosen + leak.
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Old 02-08-2016, 11:40 PM   #8
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The angle of the taper on a NPT and BSPT are the same, the difference is the shape of the thread. NPT is 60 degrees, BSP is 55. The taper is 1 in 16, both NPT and BSPT.

I fit NPT fittings in BSPT fittings all the time on old CNC equipment and a few places on my car. Works for me, but I don't really advise it.
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Old 02-09-2016, 09:08 AM   #9
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thread pitch is also off by one comparing npt and bspt

BSPT - 28 threads per inch
NPT - 27 threads per inch
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Old 02-09-2016, 11:45 AM   #10
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I've only got about half an inch of thread, im assuming thats why it threads in so easily lol
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