Replacing Fuel Line

Checked my lines and they are 5/16.

My other question is my tank has 4 outlets on the filler neck side. What are they all for? Im assuming one of them was the vapor line for the emissions. Then maybe a return line. the 4th?

Now since Im just running 1 line to the carb and no longer have a return line I can cap 3 of those. What is the 4th one for? Thanks