Thread size on older steel tanks

[jefffalcone]

I have a pair of PST LP 95s with an original hydro date of 1994 that I am looking to double up. Does anyone know the tread size on the valves?

I think the two possibilities are 3/4 unf and 7/8 unf. I found a good deal on a 7/8 unf manifold and I'm not sure if it fits or not. Any help would be greatly appreciated.

Thanks,
Jeff

 

[Jimmer]

3/4" for the LP95's. The plus is that 3/4" is WAY more common so it should be easy to find a manifold. Speaking of which I have an OMS manifold for sale. If you're interested PM me.

Jim

 

[Luis H]

The only tanks that ever used the 7/8” UNF threads were the 3500 psi (HP) tanks.
All other Scuba tanks in the US have used the ¾”NPS straight pipe thread (in the last three decades).

You will find more information on this link:
Valves, Regulator Fittings, Cylinder Neck Openings -- More than you wanted to know

Look down under the title: Cylinder Neck Threads and SCUBA Valves.

 

[jefffalcone]

Thanks Jimmer!

And I have sent you a PM.

 

[Couv]

The only tanks that ever used the 7/8” UNF threads were the 3500 psi (HP) tanks.
All other Scuba tanks in the US have used the ¾”NPS straight pipe thread (in the last three decades).

You will find more information on this link:
Valves, Regulator Fittings, Cylinder Neck Openings -- More than you wanted to know

Look down under the title: Cylinder Neck Threads and SCUBA Valves.

Thank you for the very interesting link Luis, but….that is almost everything I wanted to know about tanks and valves. Why is, "The 3/4 NPS opening is visibly larger than the 7/8 UNF opening." and "a U.S. quarter coin will fit through the 3/4 NPS cylinder neck opening but will not fit through the 7/8 UNF opening."

0.875>0.750

Tanks,

c

 

[Jimmer]

Why is, "The 3/4 NPS opening is visibly larger than the 7/8 UNF opening." and "a U.S. quarter coin will fit through the 3/4 NPS cylinder neck opening but will not fit through the 7/8 UNF opening."

0.875>0.750

Tanks,

c

7/8" UNF (Unified National Fine) is a bolt thread, that is to say that the major diameter of the thread is approx. 7/8 of one inch. The 3/4" NPSM is a pipe thread (National Pipe Straight Mechanical) and just like other pipe threads, like NPT, the dimension 3/4" refers to the I.D. of the pipe it would be used on.

Hope that explains it,
Jim

 

[Luis H]

What Jimmer wrote is correct.

The major diameter of the threads on a ¾” NPSM is a bit larger than an inch (about 1.06” if I recall correctly).