It seems my fuel tank supply line nipple is 3/8 but the fuel line is 5/16. If I use 5/16 hose it will not go on the tank fitting and if I use 3/8 it is to loose on the fuel line. What is the proper size hose ?

There is no correct hose, you have a mismatch of parts.

Is it a 440 or hemi car? If itis not then it should have a 5/16 pickup , if it is then you have the wrong body line .

Sounds like someone put a 3/8" pickup in the gas tank when it should have been 5/16". 3/8" in the tank is not good with 5/16" line because there is no good way to hook it up that I can think of.

This is 440 R/T car I have had since 73. I am sure the line and the tank are original.

If its a 440 car the line size is 3/8. It most likely has a 1/4 return line also. What did the hose look like that you removed? As said you have mixed parts.

This is my reply from dodge charger.com That's the correct (i.e. factory-correct) configuration, strange as it may seem. I've used 5/16" rubber fuel line before and just slowly worked it onto the sending unit's 3/8" stub. It ain't easy...

If you're restoring the car, a swap to 3/8" fuel line up to the fuel pump is a pretty common and fairly inexpensive change to make. The return lines are 1/4" regardless.

Do not stretch the fuel line over the 3/8 fitting. It will eventually crack and break.

Go to the hdw or parts store and buy one 5/16 male barb nipple with 1/4in Male pipe thread and one 3/8 male barb nipple with female 1/4 inch pipe and screw them together. Use the apporiate end for the size you need.

use only brass fittings.