Is stepped butting better, or would it be better to have it conical?
Are internal splines (Miyata) better, or external fluting (Gilco)?
Do the tube ends need to be thicker (butted) for brazing into lugs and filet brazing only, or can tig-welded, air-hardened steels (631, 853) make butting less relevant?
Because tubing failure often begins at a stress riser, could honing and polishing the inside of the tubes reduce the required thickness?