[mickmate]

The SCCA compliant cages I have built for ITA, ITB, and ITS calls for a 1018 or 1020 alloy DOM tube. That is a seamless mechanical tube. Make sure you look at the inside of the tube and be sure there is no seam. We have seen some cars built with ERW (Electrical Resistance Welded) tube that shouldn't have been. I am using 1020 for my frame and the stuff is hard, it rings like a bell when you rap it. Make sure it is tube, that is OD specific, not a pipe which is specified by ID. See what rulebooks call for, they update that stuff regularly based on real experience of what works.