Fuel System: Gas tank fitting

[clarkwd]

I have two gas tanks that both have a 1/2 20 thread at the tank outlet. It looks like that is an SAE O ring fitting. I was starting to work on a gas line, but I don't have fitting that will get me connected to the tank. (I probably have one somewhere, but its lost. ) Any clues where I could find another one of these or what to look for in the store?
Thanks
Bill

[karterfred88]

More likely a 1/2-20 NPT( common for a 5/16 metal line), "O" rings rarely used in that application back then. Should be able to find a combo of fittings at the local FLAPS. If you don't need an inverted flare fitting you might even try the local Hardware store, seems like their assortment rarely has any inverted, or regular flare fitting ends though..

[altair]

I would be cautious about the thread 1/4 National Pipe is 18 TPI, British Standard is 19 TPI. A machine 1/2" 20 TPI would look the same and would start in the threads and turn in several turns. Try a hand 1/2 20 TPI tap and it should turn in all the way by hand. It is possible the bung is a straight pipe thread (not tapered). I remachined a brass taper pipe fitting using a pipe die and made it a straight pipe thread and used a fiber washer on the fitting and snugged it up tight into the tank. You have to turn the die over to make it a straight thread on the brass fitting. The flair fitting on the fuel line will fit into the adapter. I tried the local parts store and there were no straight pipe fittings available, but pipe dies are available.