CFR /  Title 33  /  Part 183  /  Sec. 183.538 Metallic fuel line materials.

Each metallic fuel line connecting the fuel tank with the fuel inlet connection on the engine must:

(a) Be made of seamless annealed copper, nickel copper, or copper-nickel; and

(b) Except for corrugated flexible fuel line, have a minimum wall thickness of 0.029 inches.