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tech / rec.crafts.metalworking / Eighth-inch pipe thread puzzle

SubjectAuthor
* Eighth-inch pipe thread puzzlebob prohaska
`* Re: Eighth-inch pipe thread puzzleJim Wilkins
 `* Re: Eighth-inch pipe thread puzzlebob prohaska
  `- Re: Eighth-inch pipe thread puzzleJim Wilkins

1
Eighth-inch pipe thread puzzle

<trpj7j$2p8s4$1@dont-email.me>

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From: bp...@www.zefox.net (bob prohaska)
Newsgroups: rec.crafts.metalworking
Subject: Eighth-inch pipe thread puzzle
Date: Mon, 6 Feb 2023 00:56:19 -0000 (UTC)
Organization: A noiseless patient Spider
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Summary: Did the NPT standard change in the last century?
Keywords: npt, pipe taper standards
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 by: bob prohaska - Mon, 6 Feb 2023 00:56 UTC

Did the standard size for one-eighth NPT threads change at some
point in the past half century or so? I find myself with a few
fittings that don't seem to agree with one another.

In one group there's a fairly modern vibratory pump made in
Italy, stainless steel street tee from Cajon, some brand new
fittings bought from Ace hardware and a very small pressure
gauge that might be a century old.

In the other (too big) group are a tubing adapter from an icemaker
hookup kit, a generic hose barb of unknown origin and a hex plug.

All the male threads are visibly tapered, including those that
came with the pump, so it's not likely an NPS-NPT mixup. The
mismatch is small, maybe .002" at the big end and .006" at
the start. That rather implies a different taper, but AFAIK
all pipe threads were tapered 3/4" per foot.

Thanks for reading!

bob prohaska

Re: Eighth-inch pipe thread puzzle

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From: muratla...@gmail.com (Jim Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Eighth-inch pipe thread puzzle
Date: Mon, 6 Feb 2023 07:42:02 -0500
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 by: Jim Wilkins - Mon, 6 Feb 2023 12:42 UTC

"bob prohaska" wrote in message news:trpj7j$2p8s4$1@dont-email.me...

Did the standard size for one-eighth NPT threads change at some
point in the past half century or so? I find myself with a few
fittings that don't seem to agree with one another.

In one group there's a fairly modern vibratory pump made in
Italy, stainless steel street tee from Cajon, some brand new
fittings bought from Ace hardware and a very small pressure
gauge that might be a century old.

In the other (too big) group are a tubing adapter from an icemaker
hookup kit, a generic hose barb of unknown origin and a hex plug.

All the male threads are visibly tapered, including those that
came with the pump, so it's not likely an NPS-NPT mixup. The
mismatch is small, maybe .002" at the big end and .006" at
the start. That rather implies a different taper, but AFAIK
all pipe threads were tapered 3/4" per foot.

Thanks for reading!

bob prohaska

------------------------------------

https://wavelen.com/2018/03/15/painful-lesson-of-the-day-npt-vs-bspt/

There are two series of British pipe taps. The letters R and G are -German-
for Rohr (pipe) and Gas.
https://apporo-cnc.com/extend.php?menu_s=406&sn=54

To add to the confusion, BPT may mean Briggs Pipe Thread, which is the
American predecessor to NPT.

The nominal inch size refers to the original ID of wrought iron pipe. Modern
steel pipe has thinner walls and thus a larger ID, though stronger Schedule
80 pipe is close to the original ID. If you need to chuck a pipe fitting in
the lathe the threads on a brass nipple will run truer.

EMT conduit has the same ID as Sch 40 pipe and chain link fence tubing the
same OD, though its nominal sizes are the actual OD rounded to the nearest
fraction. Depending on the gauge of the fence tubing the two may telescope
together, I used 1" conduit with a 22 gauge shim to splice a break in my TV
antenna mast which is 1-3/8" (1.315") fence top rail, the same size as TV
mast tubing but much cheaper and easier to find.

I assembled a cone of pipe reducing bushings up to 2", with the inner and
outer NPT sizes labeled, to identify unknown threads.
hth, jsw

Re: Eighth-inch pipe thread puzzle

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From: bp...@www.zefox.net (bob prohaska)
Newsgroups: rec.crafts.metalworking
Subject: Re: Eighth-inch pipe thread puzzle
Date: Tue, 7 Feb 2023 16:43:27 -0000 (UTC)
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 by: bob prohaska - Tue, 7 Feb 2023 16:43 UTC

Jim Wilkins <muratlanne@gmail.com> wrote:
>
> https://wavelen.com/2018/03/15/painful-lesson-of-the-day-npt-vs-bspt/
>
> There are two series of British pipe taps. The letters R and G are -German-
> for Rohr (pipe) and Gas.
> https://apporo-cnc.com/extend.php?menu_s=406&sn=54
>

Aye, there's the rub...It looks like the inlet fitting on my pump is
probably BPT, while NPT fittings work ok on the discharge. Why they
(Fluid-O-Tech, an Italian company) would mix fittings eludes me.
Even better, it's part of an espresso machine made in Switzerland 8-)

The difference between 27 and 28 TPI is not readily visible and I
wasn't expecting it at all. IT does nicely explain why an NPT fitting
hangs up in half a turn. Hope I didn't damage the threads too badly...

> hth, jsw

It did indeed, thank you!

bob prohaska

Re: Eighth-inch pipe thread puzzle

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From: muratla...@gmail.com (Jim Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Eighth-inch pipe thread puzzle
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 by: Jim Wilkins - Tue, 7 Feb 2023 21:27 UTC

"bob prohaska" wrote in message news:trtv3f$3ql3k$1@dont-email.me...

Jim Wilkins <muratlanne@gmail.com> wrote: ...

The difference between 27 and 28 TPI is not readily visible and I
wasn't expecting it at all. IT does nicely explain why an NPT fitting
hangs up in half a turn. Hope I didn't damage the threads too badly...

bob prohaska

------------------
Amazon has BSPT to NPT adapters.

Do you have a lathe? When I need an odd fitting I may buy a standard one
that is correct on one side and has enough metal to cut down on the other
side. For example I've threaded a garden hose repair end to turn a trash can
into a rain barrel.

Polymer clay (uncured PVC resin) can be forced into an opening and then
heated to harden it, to measure a diameter or thread pitch.

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