Tank threads

[lenweber2]

Between my son and I we have several older breathable air tanks. We have 3-4 new tanks with the slow fill type smaller valves and want to get the same or like valves for those tanks so the output is a male fitting. Now after all that if your still with me, Is there and EZ way to tell the tread size for the valve?

 

[Motorhead]

Yes ... measure the diameter and place a thread pitch gauge on threads ... Sorry, tho am serious

 

[BigTinBoat]

Not sure when they started but DOT now does require the valve thread to be on the bottle. If it's an alum scuba tank look around the neck for it to be "punched" in. If CF tank then it's on the label somewhere.

 

[lenweber2]

Didn't want to drain them to do it. LOL

 

[Eaglebeak]

Yes ... measure the diameter and place a thread pitch gauge on threads ... Sorry, tho am serious

It can be confusing. It's very important to understand that the 3/4 and 7/8 trade descriptions do NOT indicate relative sizes of the physical dimensions of the opening! This is because the two thread forms are from two different standards, and the names used to describe them refer to only the trade size and schedule. The 3/4 NPS opening is visibly larger than the 7/8 UNF opening. For the whole story, take a look at this.https://www.divegearexpress.com/library/articles/valves-neck-threads