And a note on Mild Steel, it's not all the same. ERW is a welded seam tube, typically made from 1010 steel. It's cheap and the wall thickness is hit or miss, which is why people have to use heavy .134 wall stuff to make sure it passes tech.

DOM is much more accurate and typically made with 1020. Usually you can use .120 wall with a .118 minimum spec safely.

ERW is really crap. Running a drill bit through both materials really shows the difference in them. Both are considered mild steel, costs are different.