SurfLung wrote:I just looked up the '64-'67 catalogs... Still no mention of 1/2" O-Ring valves but they introduced a 15/16th valve and the picture looks like what I am always thinking is a 3/4" valve. The pictures of their 3/4" valve still look like 1/2"... What was actually the standard for them? Was their 3/4" actually what we're calling the 1/2" Straight Thread O-Ring?
The confusion is understandable, and is caused by the difference in stating pipe measurements versus all other types of threads. Tapered Pipe thread(NPT)sizes refer to the nominal inside diameter (ID)of a given size of pipe, so the actual outside diameter is larger.
That's why a 1/2" pipe thread valve has an outside diameter (OD) of about 3/4" at some point along the taper. To add further to the confusion about NPT, the ID of a pipe can vary considerably from the stated size with different pressure ratings of the pipe, and the OD is always remains the same for all practical purposes.
Straight threads are
usually rated by the outside diameter, but there is actually a Straight Pipe Thread that is rated like pipe sizing. So when Sportsways referred to their 1/2" threads, those were the tapered pipe thread valves, and when they refered to 3/4" valves they were referring to the straight 0-ring sealed threads of the tank neck ID. When they referred to the 15/16" valves, that was a reference to the ID of the opening of the more modern tanks... not to an actual pipe thread size. That size is what is still used in most Scuba tanks today, and I think they are actually a 3/4" Straight Pipe Thread with an o-ring seal (even though the OD of those threads is well over one inch). Had enough?
So Sportsways was not using standard conventions when referring to their thread sizes, thus causing a danged lot of confusion.
I hope I got that right, and if not I would be glad to hear corrections.