Stock fuel line size? And some questions on fuel line.
 

As the title says, what is the size of the stock fuel source and return lines?

Also, why is the return bigger than the source? Shouldn't it be the other way around?
(If it is the other way around, ignore this question.)

What would be a good material to use for fuel line? I've never had to replace the hard lines in a car before. Just curious. Is it available from the local parts store? I've never seen it.

Is there any point to cooling fuel?

Bump