UK vs US threads?

@hot rod
Do you have couplings that are 1.25" BSPT x NPT?

Ironman said:

@hot rod
Do you have couplings that are 1.25" BSPT x NPT?

A nipple like this, or a union fitting?

Question:

Does the BSPT nave the same screw pitch in inches as NSPT?

With what appears to be 1/8" NPT in inches has 28 Threads Per Inch according to a screw pitch gauge. Bit the BSPT has 27 TPI. Or the other way around. If you run a 1/8" NPT pipe tap to clean out the scuzz in a 1/8" BSPT, they wreck the threads.

I had a inch/metric tap and die set and it had both sets. Not until I put a screw pitch gauge on it could I tell. That, and you couldn't run a tap in more than a couple of turns before it started cutting. Not so with the proper sized tap.

Just asking.

The problem with trying to mate British to NPT is the that the angles are different. Sometimes the pitch and size can be close or the same but the British thread is based on a whitworth 55deg round crest and NPT is based on 60deg flat crest. This is why depending on the size/pitch relation between the two types driving a tap into it works. Good time to get a lathe to solve this problem.

Ironman said:

Female threads. A union or coupling would work.

I have a plate HX that has 1.25" BSPT nipples and need to get to NPT.

A standard NPT coupling with some anaerobic thread locker might take care of it.

You can get a 1" X 1 1/2" bushing and drill and tap the 1" side to 1 1/4" British.

Which piece on p.93?

It's a little confusing.
A 1/2 BSP nut fits 3/4 NPT
3/4 nut fits 1" NPT
1" nut fits 1-1/4 NPT
1-1/4 nut fits 1-1/2 NPT

then select the tailpiece either NPT or sweat, add a green fiber gasket.

So if you had a flat plate HX with 1" NPT thread page 92 shows some options.

If you connect onto a NPT pipe thread, for example, file or sand the end flat so the gasket seals.

So here is an example

A 1" brass street ell, with a sanded face for the gasket to seal against.

A 3/4 nut and a tailpiece, or 3/4 SolarFlex with a flattened end, would fit to that..

Below are nuts from 1/2- 1-1/2

Some can be used with reducing tailpieces as the one shown, which also has a hemp thread.

@Handi.

You don't have to have a taper attachment for a lathe to cut tapered threads. You can turn the piece on center and move the tail stock off center to attain whatever taper you desire. Off course this is a pain because you constantly have to reset center on the tail stock later if you need to use it for it traditional purpose.

I cut threads for pipe nipples at 3" or above on my manual Lathe with a bull nose center. It does have the taper attachment making life much easier. I also use it for piping oddball fittings, like recently a flush face pipe plug for a convection radiant radiator to clear the incoming steam line. By far my most favorite tool in my arsenal.

I am pretty sure only unified 60deg thread is flat crested and not pointed (which NPT falls under). It was pointed when it was American standard thread but was changed to flat crested unified after WW2 to reduce stress risers. The British whitworth thread was thread for thread stronger than American standard thread because they had the rounded crest reducing stress risers so the unified thread flattened the crest. At least that's what I remember from an old machinist handbook somewhere.

Handi said:

hot rod ...I think I now understand what you were trying to explain . It took me a while to get the hang of the Caleffi catalog that was posted .. If the catalog would call out their BSPT sizes the same way the call out the NPT thread it would simplify things ..
Here are a few examples of the way the catalog works ( I think !)

From page 76 of the Caleffi catalog -
Double nipple - code NA12122 —> ¾" X ¾" male
( I believe this to be a BSPT- (British Standard Pipe Taper)

Not to be confused with the similar looking fitting just below it which is :
Double nipple - code NA12172 —> ¾" NPT X ¾" NPT
(there is no question about what this is )
So if one were looking to go directly from NPT to BSPT ( or vice versa) here are some examples that might work.
From page 77 of the same catalog . -
code —> NA10064 - 1" NPT X 1" male thread.
——or ——
code — > 61215A - 1"NPT (female) X 1 ¼"( male) Threaded bush.
( I believe these to be adaptors that go directly from NPT -> BSPT.)
I hope I got it right .. if not then a call to Caleffi in WI. might explain things .

Correct unless it states NPT, it is a BSP. Sorry about the confusion, marketing took over, and they are not plumbers

We do have some transition nipples page 92 for example NA10064 is a NPT X BSP in 1"

The BSP end has a wide face so a fiber gasket can seal. Most of these were developed for SolarFlex adapters, which seals with a fiber gasket.

Handi said:

too bad not many young ones are following the machine shop trades . In a few years it will die out ..Glad to see the plumbing trade still is attracting a rather large following . there's nothing better than a lathe with full attachments it can work wonders in the right hands ..
Thanks for the reply..

Yep agreed but on the bright side when it dies out I will be able to purchase a Monarch 10EE for less than $500 bucks on ebay and kick my SB13 to the curb. Can't wait to explain to my wife why I have chain falls in my kitchen trying to rig the biggest piece of cast iron ever created for a 10" lathe into my basement.

@Hotrod . Sorry, but when I click to link it says "page not found".

Never use a NPT thread on a BSP thread. You will damage the thread and it isnt a sustainable seal. there are plenty of suppliers offering british metrics in the states (BrittischMetrrcis, Swiss Fittings AG etc.)