[vettestr]

Hey Boxhead,
NHRA specs for a roll bar are = A roll bar must be at least 1 3/4 inch outside diameter and have a wall thickness of at least .118" for mild steel tubing or .083" for chromoly tubing.

I offer this only as a starting point as this NHRA rule means nothing for your requirements. I make mine out of seamless chromoly 2" OD with a wall of 0.120". A material spec is 2.000” x 0.120” CDN/4130/Seamless or ASTM 1018/1026 CDS/DOM .

ERW tube is cost effective and nice to work with. Have fun Jeff C