if you look here

http://www.appliedracing.com/tubing-and-plate/tubing-dom---mild-steel---4130/

you will see they have CM/DOM/and mild steel and if you look at there cage kits there standard options are CM or mild steel which is ERW.

70 duster full chassis super pro 416 CNC Indybrock heads 727 w/brake

best so far 1.212 60 6.219 in 1/8 at 110.88 9.768 at 137.81 1/4