NGWClub®, Inc.

Hi,
Before I actually spend money I would appreciate confirmation of a thread size. I think the oil pressure switch thread is 10mm fine. Is this correct, please?

actually it is 1/8 British pipe thread. which is very close to NPT but can be difficult to start a fitting in. Technically it is 1/8 28 BPST,( BSPT ) . and 1/8 NPT is 1/8 27 NPT. so very close with slightly different taper and one more thread per inch. . Many use standard 1/8 NPT but be careful starting the fitting and do not over tighten.

that's crazy.

salukispeed wrote:actually it is 1/8 British pipe thread. which is very close to NPT but can be difficult to start a fitting in. Technically it is 1/8 28 BPST,( BSPT ) . and 1/8 NPT is 1/8 27 NPT. so very close with slightly different taper and one more thread per inch. . Many use standard 1/8 NPT but be careful starting the fitting and do not over tighten.

Well I'll be danged. Thanks Sal. Back in 1970 or so I put an oil pressure gauge on my CB750 using a brass tee. It seemed the Japanese part was the same tpi but was slightly narrower. I stuck a tap in the engine and widened the hole to accept the tee fitting. It worked fine (and is still there). But I never realized the tpi difference. I have a metric tap and die set I bought from Sears back in the 70's (when their sets were actually good quality) and it has 1/8" tap and die in it. I checked and the inscription says "1/8 BSP" which I now realize is British pipe thread. I'm currently doing a similar tee adaption on my GL1000 and glad I read your wisdom. I used my Craftsman tap and die to 'nerf' the threads in the right direction and got everything to fit. It looks like the VDO fittings are the same as the Japanese. So my guess is that the world uses British pipe thread and we have our own. Thanks for the enlightenment.

Isn't that interesting. Thanks for the history Salukispeed, that could go straight to Wikipedia! And the Ancient British engineering is still staggering on.

I am commenting from memory if anyone would like to confirm would be good too.

I have always used the standard brass fittings that come with the gauges. And always found one that worked fine. Never checked thread size, pitch etc. However I have run a tap into the hole from time to time. Never had a leak,...but I do use Teflon tape on the threads

CYBORG wrote:I have always used the standard brass fittings that come with the gauges. And always found one that worked fine. Never checked thread size, pitch etc. However I have run a tap into the hole from time to time. Never had a leak,...but I do use Teflon tape on the threads

I'm going to use thread sealer on account of a worry that a piece of that teflon could get in the line and do some damage a-la-RTV. I use teflon tape in plumbing applications and have seen how it shreds.

Ya,...you can't over do it. I make sure the tape is on the threads, and not the end of the fitting where the hole is. May not even be needed, But better safe then sorry

I always used Teflon in engine shops. I never put it on the first few threads. and break the tape while pulling away from the hole end close inspection.

I did some more useless searching on this size fitting difference. And after it all it usually works
WARNING: Never, never try to mate a BSP fitting with an NPT or NPS fitting if the pressure holding capability is at all critical.

NPT/NPS and BSP threads are not compatible due to the differences in their thread forms, and not just the fact that most diametrical sizes have a different pitch. NPT/NPS threads have a 60° included angle and have flattened peaks and valleys (this is a Sellers thread form); BSP threads have a 55° included angle and have rounded peaks and valleys (this is a Whitworth thread form).

NPT and BSP thread pitches (threads per inch, TPI) are listed below. To determine pitch, use a thread gauge or count the number of threads that fall into a 1" span. Note that, strictly speaking, when we use threads per inch, we are actually specifying the inverse of the pitch, pitch being in units of [length] / [peak to peak]. Metric threads are usually specified in actual pitch, e.g., 1.5mm, 2.0mm, etc. This is the actual length of each thread, peak to peak. Although the term "pitch" is universally used, albeit loosely, to describe threads per inch, the actual pitch of a 1/4BSP fitting is really 1/19 inch, or 0.0526 inches.


Pipe Size
Pitch (Threads/Inch)
NPT/NPS
BSP
1/16"
27
---
1/8"
27
28
1/4"
18
19
3/8"
18
19
1/2"
14
14
5/8"
---
14

Pipe Size
Pitch (Threads/Inch)
NPT/NPS
BSP
3/4"
14
14
1"
11 1/2
11
1 1/4"
11 1/2
11
1 1/2"
11 1/2
11
2"
11 1/2
11
2 1/2"
8
11

Pipe Size
Pitch (Threads/Inch)
NPT/NPS
BSP
3"
8
11
3 1/2"
8
11
4"
8
11
5"
8
11
6"
8
11
8"
8
---

Some people have too much free time on their hands....

OOps!! Did I say that out loud?

You read my mind

Well maybe so but I found the pipe thread information very helpful. I'd just chalked it up to Japanese vs Amrrrrcan, shrugged and figured 'wadda I know' since 1970

buy an edlman 265220 adapter then buy a 1/8 npt switch