Brake line tube diameter question

Got to be who the supplier was in your area for the assembly line. I just texted a buddy of mine who has been in and out of the dealerships as a mechanic since the 80s. He said they were brass when the cars were new, and later ones they machined em out of aluminum or some type of potmetal. We are in Texas. I think in the 80s G bodys were made in Arlington, D/FW area. Trucks are made there now.