Technical What size/style fitting for 49-54 chevy fuel outlet

What size and style/thread fitting is this on a factory 49-54 chevy tank?

 

this place sells new lines
http://www.truckandcarshop.com/4157.html

 

Be careful! when I put in a new tank the fitting was different that the original one. I don't remember the sizes. But make sure you get it right before you put a full tank of gas in it.
-Pat

 

I'm just looking for the size and specs of the fitting that gets put on the line with flared end that threads. I'm trying find an adapter for the threaded insert in the tank.