I seem to recall there is an alternative thread to 1/8" NPT that is very similar. Does anyone remember what it is?

Im asking cos Guiness wants to borrow one. I dont have NPT but do have BSP, UNF, UNC, BSW, BA etc etc taps in my newly aquired collection.

cheers,
Darren.

1/8 bsp is basically the same but without the taper

Cheers Darren

The thermostat housing on the Kawasaki is Cast Ally with a metric sender in there at the moment. I have an aftermarket sender that is 1/8" NPT 27 TPI.

What I want to do is drill out the metric threads and re-tap to suit the new sender.

Nat, would the 1/8 BSP be ok, or do I run the risk of water leaks and or spliting the housing when I tighten the sender into the hole?

Cheers

Mike

Cheers Nat.
Does that mean if you have a 1/8" npt gauge to fit in an engine block that is tapped 1/8" BSP it should secure and seal OK with some thread seal?

Ooops - Dual posting, i should have waited!!??? Hope you dont mind me stealing your question Mike, i thought you were out of the office earlier when i called.

[Edited on 25/10/06 by DarrenW]

[Edited on 25/10/06 by DarrenW]

Be very carefulmixing BSP threads with NPT. The BSP is 28tpi, whereas the NPT is 27.
Not much in it but I wouldn't do it.

I've just sorted this exact problem myself...

1/8 NPT is 27 threads per inch and 1/8 BSP is 28 TPI...

An 1/8 NPT male fitting is not ideal for an 1/8 BSP female thread though. I wasn't satisfied that the seal would be good enough (and was advised that I may end up with a small leak). This can be solved with the use of a little PTFE tape, but again isn't the best solution.

I used an 1/8 NPT to 1/8 BSP converter in the end to make sure everything was sealing as designed. And this worked fine.

For your application Guiness I would personally source a male 1/8 BSP to female 1/8 NPT fitting, assuming your gauge is a female 1/8 NPT thread. These cost a couple of quid from a local hydraulics hose fitters.

Chris.

Or obviously get a metric (M10 x 1, maybe) to 1/8 NPT converter?

Chris.

Thanks guys

I could get an adaptor, but it's for a water temp sender, and the current one sits nicely in the flow of water, if I put it in an adaptor I think I might get issues with the ally body heating up transfering the heat to the brass adaptor then to the sender and having a pocket of still water might lead to dodgy readings?

Cheers

Mike

Very true Guiness... This was for my oil pressure gauge so shouldn't have an effect on the readings...

I personally would invest in an 1/8 NPT tap!

Probably no help there at all then!

http://www.nfauto.co.uk/tap_die_set.htm

Chris.

Personally I'd invest in something a little higher quality than that set. Hopefully this one would be better (HSS):
http://cgi.ebay.co.uk/HSS-NPT-Tap-1-8-x-27-TPI-Tap_W0QQitemZ150028397899QQihZ005

I was hoping to avoid buying another single use tool. Which was why I asked if I could borrow one.

When I started my build I had a set of spanners and a socket set. Now I have tools all over the place, most of which only got used once or twice! Including some things I bought twice 'cause I couldn't remember having one, or having broken one!

Mike

quote:

---

Originally posted by Guinness

if I put it in an adaptor I think I might get issues with the ally body heating up transfering the heat to the brass adaptor then to the sender and having a pocket of still water might lead to dodgy readings?

---

I think you're overthinking it, I'd give it a try before I started retapping and possibly causing other problems.

I have heard of people that have done this and it affects the readings by lagging them slightly... I think on average it's as accurate, but not as responsive.

You could try it and see? Adapters are very easily sourced at a quid or so from most hydraulics places.

I know what you mean about single use tools though!!

Still, they are assets for life!

Chris.

Leaks happen with adapters as they are tapped/thread rolled not thread formed (Single point CNC cut). With a taper tap or external chasers the tool leaves a witness mark all the way down the thread, hence a potential leak.

Over the gauge plane of the 1/8 NPT or 1/8 BSPTr the accumulative thread pitch error is insignificant. Use PTFE tape and rest assured it won't leak. We've done exactly the same thing with no leakage problems (yet).

The thread form of the NPT (60) and BSP (55) threads respectively forces the PTFE into the vacant forms and radii and makes an excellent multi-seal.

OK, don't think I've ever been accused of over thinking anything before!!!!

I'll look at getting an adaptor, but that's going to mean finding out what thread current sender is first, rather than just getting a drill out!

Mike

Buy an 1/8NPT tap. Just a carbon steel one will be enough for one job and will only be a couple of quid.

If a jobs worth doing...

David

For what it's worth I would be quite happy mixing NPT Taper and BSP Taper fittings up to 3/8" without worry, 1/2" and above becomes a bit dodgy. Always use
PTFE tape, 3 to 5 wraps applied clockwise looking at the narrow end of the fitting.
Best of luck Davie

I had to buy a 1/8NPT tap to get around my experience with an easiout.
I did have a 1/8 npt in the set that I got from nfauto, but to be honest it couldn't cut a thread through melted butter.

quote:

---

Originally posted by daviep
For what it's worth I would be quite happy mixing NPT Taper and BSP Taper fittings up to 3/8" without worry, 1/2" and above becomes a bit dodgy. Always use
PTFE tape, 3 to 5 wraps applied clockwise looking at the narrow end of the fitting.
Best of luck Davie

---

You can also get BSPT threads,
British Standard Pipe Tapered thread.
Cheers John