Pappy's right.

Mild steel SFI specs. ......
For round tubing larger than 1 1/2” diameter, the nominal wall thickness is .118”
For round tubing 1 1/2" or smaller diameter, the nominal wall thickness is .108”
Exception: for round tubing used for helmet guards (#49 and #50) and cage gussets (#34, #35, and #36), the nominal wall thickness is .083”
For rectangular tubing 2” x 3”, the nominal wall thickness is .083”
For rectangular tubing 2” x 2”, the nominal wall thickness is .065”
Plate thickness and bolt diameters are minimum requirements, unless otherwise specified