67 Barracuda 273 Fuel line thread size???

If you mean "pipe" diameter, it is 5/16"
yes, first time ever doing a build, thought for whatever reason when I read 5/16 or 3/8 I automatically thought thread but the guy at Jegs sold me a 3/8 being that I don't have a return line coming from some charcoal canister. He said if I had a return that would be a 5/16, I already bought it and now just waiting on it, am I missing something here? Would I still be able to use the 3/8 already purchased? and Thanks for the reply mopardude62