Re: Cromor - When I took a TIG framebuilding class in the early 90's, we used Cromor. I don't recall the specs, but it's butted 4130 with wall thickness probably in the .9-.6-.9 mm range... I can remember burning holes in 0.8 mm tubing and deciding that was too challenging for my beginning welding skills. Diameters are modern "OS" oversize, not the older 1" standard. It's not Columbus' fanciest stuff - at the time that was Nivacrom, IIRC.. but Cromor is a good workaday tubeset, not unlike Reynolds 531.

Edit: Columbus tubing lineup from 1989