I standardized on full-soft stainless partly on the basis that it is rated for single flares whereas aluminum (at least in some sizes) is supposed to be double flared, or so they say in the aircraft world. Also more resistant to dents from dropped tools, scratches on the flare surface, etc. And no corrosion.If we needed to make these out of a hard line. What material would be accepted race car practice. ALuminum, Stainless steel, copper, other? For that matter what material would you guys recomend to run oil in a hard line to and from a cooler for instance.