I swapped motors a while back, and im trying to do the fuel line right since I didn't know there was a real difference between the cheap connections and the expensive ones. My 89 firebird originally came with an lo3, and now has a carbed 350.

I've got everything i need to put the lines together, except the adapters for the stock lines. I want to use the stock lines from the tank to the engine bay, then connect there and use russell line.

I've looked at a ton of posts, but have never seen anyone say what the size of the stock lines are. I have seen a picture of someone using a similar setup, but no documentation of the exact size of the lines.

I'm using Russell ProClassic line and adapters in AN 6. I'll use any color if it works, but I'm trying to stay away from the red/blue.

 

I belive they are 3/8", but to be sure you can just put an open end wrench on the line itself just for measurement. The lines are measured as O.D. (outside diameter). A wrench is cheaper then a micrometer, and suffices for non-percise work.

 

I'm not worried about the outer diameter, I need the thread size. I had to use 2 different sizes for the 2 lines. I cant remember what the sizes are, and they're the cheap ones from the car parts store, so there's no size printed on them. I found the picture of where they connect.
I don't necessarily need the same 120 degree fitting, just the size of those threads. "an -6 line to ?"