Measure valve thread, please ?

[Externet]

Hello.
Anyone with a valve removed from the tank at the moment; can you please measure the thread in your valve, not what the documents/specs may show on a web site link ? (a parallel one, not tapered)
Is it 0.700" or 0.740" or other ?

 

[herman]

There are at least 4 straight threads that I am aware of that were used in scuba tanks, 1/2 NPT, 3/4NPT, 3/4 BSPP and M25. All are different and the last 3 are pretty close to each other so you need to be very careful when trying to figure out which you have.

 

[txpolo]

In addition to Herman's comment (He's usually right from what I've seen here on SB. He knows his stuff.) there is also the slightly less common 7/8 straight thread that is on some of the 3500 psi tanks. Ironically it's actually smaller than the 3/4 NPT thread... go figure. It's 0.875-14 UNF which seems larger than what you're measuring... you sure it's not a tapered thread?

 

[Externet]

Thanks, fellows. Is not tapered. To add confusion, Wikipedia mentions a thread 3/4" x 16 UNF, which I have to suspect the 3/4" is not from measuring the thread, but one of those plumbing 'nominal' names.
What cylinders use the 3/4" x 16 UNF ? Do you know ?

Is there a valve for such 3/4"x16UNF ?
Seems there is nothing NPT

 

[runsongas]

3/4 UNF is a CGA 870 valve

Sherwood Post Medical Oxygen Valve - CGA870 .750" UNF | Gas Cylinder Source

 

[Externet]

Thank you, runsongas. Interesting a medical oxygen cylinder being listed in Wikipedia under diving cylinders.

 

[Bob DBF]

Thank you, runsongas. Interesting a medical oxygen cylinder being listed in Wikipedia under diving cylinders.

Some people don't know what they have, and guess. Buy a foreclosed storage area, or clear out a relatives house. I've got some good deals because s seller, from his POV, is just getting rid of crap.


Bob

 

[herman]

3/4-16 UNF would be .750 since the UNF indicates its a screw thread dimension rather than a pipe thread.
I forgot about the 7/8. You have to be careful with valves since some will "almost work". If I remember correctly, the M25 will loosely thread into a 3/4 NPS but will come out under pressure. The 3/4 BPS will thread into a 3/4 NPS a few turns but stop......took me days to figure this one out. The size looks the same but the 55 deg threads jam after a few turns, you have to look hard to see the difference in 55 and 60 degree thread.

 

[captain]

Herman is correct 3/4-16 UNF is a bolt thread just as 3/8-28-4 UNF used on PL hose connections is the same as what is commonly referred to as a fine thread as opposed to course thread. A 3/8-16 UNC is coarse thread.

UNC and UNF - Unified Inch Screw Threads