NPT thread

This topic has 10 replies, 8 voices, and was last updated 4 July 2026 at 15:46 by Dave Halford.

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3 July 2026 at 13:45 #854555
Bill Dawes
Participant
@billdawes
Hi guys, sorry if I should have put this thread somewhere else.

My son asked me if i had a spare mixer tap, dug into the depths pf my old plumbing bits box and found one.

It does not have any tails in it but I just happen to have a 1/8″ NPT tap, tried this and it screwed in perfectly, however tails i have looked at seem to have 10mm and 15mm fittings.

A 10mm screw certainly doesn’t fit, any ideas?

Bill D.
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3 July 2026 at 14:54 #854558
Neil A
Participant
@neila
The thread on the ends of flexible pipes for the mono tap are M10 x 1 constant pitch thread. Not ISO course thread.

https://www.wolseley.co.uk/wcsstore/ExtendedSitesCatalogAssetStore/images/products/AssetPush/DTP_AssetPushHighRes/std.lang.all/wi/ng/236550_CMFTCW-1510300%20correct%20drawing.pdf

I hope this helps.

Neil
3 July 2026 at 14:58 #854559
Macolm
Participant
@macolm
In cases like this, I usually buy a couple of brass fittings with the correct thread, and bore out or turn the mating feature so as to solder on lengths of 10mm or 15mm pipe. Secure the threads/pipes to the mixer, making them watertight, fit the mixer in place, and continue the plumbing with compression fittings.

Doing it this way minimises the number of incompatible plumbing fitting you accumulate!

I do presume you are a certified government approved mixer tap installer?
3 July 2026 at 15:11 #854560
Bill Dawes
Participant
@billdawes
Macom, are you the guy that played the union convenor in Carry on at your convenience.

Bill D
3 July 2026 at 15:20 #854561
JasonB
Moderator
@jasonb
Unlikely to be NPT unless in America as UK, European and a lot of the rest of the world use BSP also known as G thread over the channel. 1/8″ BSP is quite common on fitted tails and a modified 10 or 12mm to 15mm pipe compression fitting can be used to join to these if you turn the end of the olive taper flat to suit the flat washer on the tail

Taps if threaded for tails are usually M10 or M12 x 1 with a recess to take an O ring seal.
3 July 2026 at 17:22 #854579
vintagengineer
Participant
@vintagengineer
Could be BSPT
3 July 2026 at 19:16 #854607
DC31k
Participant
@dc31k
On 3 July 2026 at 15:20 JasonB Said:

1/8″ BSP is quite common on fitted tails

I think there is a typo. there and you wanted to write 3/8″ BSP.

These are the fittings that go into the end of a 15mm compression isolator valve to accept the tails:

https://www.screwfix.com/p/tesla-brass-compression-adapting-flexible-tap-connectors-15mm-x-3-8-2-pack/6089R
3 July 2026 at 20:07 #854621
JasonB
Moderator
@jasonb
No as someone who earns a good proportion of their living fitting bathrooms and kitchens I mean modifying a compression reducer like this as it is harder to find 15mm to * BSP in the smaller sizes. 3/8″ to 15mm are easy to find so no need to use the adaptors you show.

It is when you have smaller female threads on the end of the tails that I modify a fitting like this, taking off the compression nut and olive from the small end and facing the end flat so it does not cut into the washer. That’s actually 1/4″ BSP but some of the high pressure basin taps come with smaller 1/8 threads, no good for UK gravity fed systems unless you pump them. I’m holding the end that would take the 15mm compression nut
3 July 2026 at 20:24 #854623
JasonB
Moderator
@jasonb
These two were 1/8G, made to order from a Spanish firm, about 10 week lead in time and £1800 each. Horrible taps as they had a tiny “joystick” type control that was really hard to use with wet hands but the Client liked the look.

The solid glass basins were equally impractical as they could not be fitted with a plug just the custom grill type waste and you could only trickle a small amount of water otherwis eit splashed everywhere if too fast.

The counter is a single ceramic tile that was 1000 x 3000 again special order from Itally along with the 1000x 400 wall tiles . All are just 3mm thick. I did get my stone people to cut the larger tile for me as it was a bit big for my cutter!

They put up with it for about 18 months then had me back to fit taps I suggested and a one piece Corian top with two integral basins.
3 July 2026 at 23:30 #854665
Bill Phinn
Participant
@billphinn90025
Jason’s clients clearly prioritised form over function…until they realised their mistake.

At least we can be sure it was fitted well in this case. Too often clients go into bathroom/kitchen showrooms, say “I want that”, and “that” ends up getting fitted by monkeys, and not trained ones either.
4 July 2026 at 15:46 #854732
Dave Halford
Participant
@davehalford22513
On 3 July 2026 at 15:11 Bill Dawes Said:

Macom, are you the guy that played the union convenor in Carry on at your convenience.

Bill D

More likely ‘The Rag trade’ Everybody art.
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