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Author: Subject: 1/8 NPT or M10x1?
JC

posted on 10/11/17 at 02:01 PM Reply With Quote
1/8 NPT or M10x1?

Hi all,

I have the temperature sensors that came with my Koso digidash. I thought (assumed) that they were M10x1 thread....

Unable to find sensibly priced inline housings in M10, I ordered 2 with 1/8 NPT thread and intended to use adapters from CBS. On a whim, I just tried the sensors and they fit quite nicely....

Is 1/8NPT very close to M10x1 i.e. could they feel like they fit when they don't?

Secondly, should I use PTFE tape on the thread as per domestic plumbing?

Thanks folks!

JC

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neilp1

posted on 10/11/17 at 02:40 PM Reply With Quote
I'd check with the manufacturer for the correct size is as 1/8" NPT is a tapered thread so you will get a start if it's in M10 but it wont seal.
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voucht

posted on 10/11/17 at 03:02 PM Reply With Quote
Normally, M10x1.00 is a straight thread, and 1/8NPT if tapered. That should be enough to identify them. Although my hydraulic brake switch (from VW Beetle) has a tapered M10x1.00 thread, which is very odd and very unusual.

The complete name of 1/8NPT is "1/8x27". The "27" means "27 threads/inch".
M10x1.00 has 1 thread/mm, so 10 th./10mm.

I guess they can feel like they fit when they don't because they are very close to each other. 27 th./inch means 1 thread every 0.941mm.

If you have an accurate caliper, you can measure the distance between 2 threads. If it is exactly 1mm, it is M10x1.00, if it is a little bit less, it should be 1/8NPT.

Or you can count the number of threads on a 10mm length:
- If it is 1/8x27, you should count more than 10 threads on 10mm, actually, between 10 and 11 threads (10,63 to be exact)
- If it is M10x1.00, you should count exactly 10 threads on 10mm.

I doubt the threaded part of your sensor is long enough to count the number of thread on 1 inch, where you should find 27 threads if it is 1/8NPT and between 25 and 26 threads (25.4 to be exact) if it is M10x1.00

If your adaptor has a straight thread, a copper washer is enough to seal. If the thread is tapered, you must use Tefelon tape.

Hope that will help





Sylvain
http://vouchtroadster.blogspot.se/

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JC

posted on 10/11/17 at 03:53 PM Reply With Quote
That’s perfect! Best counting glasses on then! Thanks!
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Davedew

posted on 10/11/17 at 05:27 PM Reply With Quote
My Acewell dash came with an 1/8th NPT temp sensor.

Tapped an M10x1.0 hole and screwed it in with some PTFE tape.
Been like that for 3 years on the road and not a single problem.





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russbost

posted on 10/11/17 at 05:39 PM Reply With Quote
The reason Acewell supply 1/8 x 27 npt is that being a tapered thread it is close enough to m10 x 1.0 & 3/8 x 24 that with ptfe tape, it will go into either & form it's own seal, you are basically doing the opposite putting a straight thread into a (very close in thread pitch) tapered hole, so, again as long as you use a few turns of PTFE I can't see why it wouldn't seal. If you are going to bother to try & measure then just measure the thread diameter, m10 x 1.0 is around 9.8mm, 3/8 x 24 is around 9.5mm & the tapered thread should be quite obviously tapered if measuring with any sort of accuracy at all - you should be able to visually see the taper quite clearly

HTH





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JC

posted on 11/11/17 at 05:14 PM Reply With Quote
Thanks Russ, thanks all!

Amazing how often the bleedin obvious is staring you in the face and it takes the helpful hints on here to make you realise!

I took my calipers to the sensor but used them as paralle guides along the thread and yes, you guessed, its tapered! Problem solved, money saved!

Thanks again - at this rate I might have a running car soon.....

JC

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