5/16" - Fuel Line
$$$ - $107+ a roll - Federal Hill - measured wall thickness of .030", website says .028" - labeled to meet SAE J1650 (The standard for seamless copper/nickel hydraulic BRAKE line)
$$ - $66+ a roll - Bel-Metric - Same wall thickness as above (from other PP User)
$ - $44+ a roll - Amazon (AGS) - measured wall thickness of .025" - no printed specification on the line!
3/16" - Brake Line
$$$ - $60+ - Federal Hill - labeled to meet SAE J1650 (See above)
$$ - $38+ - Bel Metric - Not ordered yet
$ - $28+ - Amazon (AGS) - Not ordered yet
I don't necessarily plan on ordering all these, so if someone has some laying around and wants to measure the wall thickness (of a clean cut!), please do and I'll put it here.
Picture of 5/16 showing the difference between the Federal Hill stuff vs. the Amazon (AGS) stuff