Conshelf 22 port sizes

[Angelo Farina]

From another thread:

UNF 3/8-24 - regulator to hose thread for IP
UNF 5/8-18 - thread for Spareair or paintball tanks
UNF 7/16-20 - HP thread in regulator or SPG (Surface Pressure Gaufe)
UNF 9/16-18 - Thread between 2nd stage and hose

Threads in diving regulators etc, o-ring sizes

OK, so all these measures are UNF (UNified Fine pitch), whilst the measures of our local inch adaptors for compressed air, gas or water are BSPT (British Standard Pipe Taper). I am searching info on this standard, it appears that the nominal diameter is not the OD of the screw, instead it is the inter diameter of a standard iron pipe over which the screw is threaded.
A 3/8" BSPT nipple has 19 threads/inch.
Instead an American NPT nipple has just 18 threads/inch, and slightly larger diameter.

In conclusion, there are three different threads, all called 3/8":
UNF 3/8, 24 TPI, OD=0.369"
BSPT 3/8, 19 TPI, OD=0.656"
NPT 3/8, 18 TPI, OD=0.675"

What a mess!

 

[Couv]

What a mess!

Indeed.

 

[Zef]

OK, so all these measures are UNF (UNified Fine pitch), whilst the measures of our local inch adaptors for compressed air, gas or water are BSPT (British Standard Pipe Taper). I am searching info on this standard, it appears that the nominal diameter is not the OD of the screw, instead it is the inter diameter of a standard iron pipe over which the screw is threaded.
A 3/8" BSPT nipple has 19 threads/inch.
Instead an American NPT nipple has just 18 threads/inch, and slightly larger diameter.

In conclusion, there are three different threads, all called 3/8":
UNF 3/8, 24 TPI, OD=0.369"
BSPT 3/8, 19 TPI, OD=0.656"
NPT 3/8, 18 TPI, OD=0.675"

What a mess!

I don't disagree with you on your comment that it is a mess but in the US I don't think one comes across BSPT too often, and I have seen some ridiculous engineering design choices come out of your home country in a few industries.

-Z

 

[Angelo Farina]

I don't disagree with you on your comment that it is a mess but in the US I don't think one comes across BSPT too often, and I have seen some ridiculous engineering design choices come out of your home country in a few industries.

Yeah, it is called "Italian fantasy".
You have to go to Germany if you want solid engineering with no frills.
However, sometimes from these ridiculous inventions some great innovation comes out...

 

[GJC]

I have never encountered a problem with thread size differences that could not be solved with either a bigger wrench or a bigger o ring.

 

[Zef]

I have never encountered a problem with thread size differences that could not be solved with either a bigger wrench or a bigger o ring.

I would hate to be anywhere near the place when your tanks are being filled.

-Z

 

[GJC]

I would hate to be anywhere near the place when your tanks are being filled.

-Z

Tank fills are no problem. Interesting things sometimes happen when regulators are pressurized though.

 

[larsdennert]

The 3/8” can refer the diameter of the passage for fluid or air not the size of the threaded portion.

A 3/8" unf fitting might have a 1/4" passage and use a 1/4" hose.

In addition there are bspp and npp parallel threads instead of taper. Then the fittings have different sealing methods such as compression or o-ring

 

[Bob DBF]

In conclusion, there are three different threads, all called 3/8":
UNF 3/8, 24 TPI, OD=0.369"
BSPT 3/8, 19 TPI, OD=0.656"
NPT 3/8, 18 TPI, OD=0.675"

What a mess!

There are several more if you start looking for them, I made that mistake and was reading for an hour or so. It seems over time threads were made and developed for specific needs and industries. There were quite a few different standards in the US, but were standardised during WWII for parts interchangeability. I’m sure this happened in other countries as well.

Some of the old style threads hang on for special applications and for some industrial machinery that’s still hanging on.

My personal favourite is the Acme thread. And this is not just because Wile Coyote made the name famous.


Bob