What about slab thickness?
I used 1" square tubing, to build my mill. With 3/16" pads on the bar clamps, about the thinnest slab I can mill is 1-1/2".
I am thinking about adding shims(pads) to the base, to allow me to mill a thinner slab.
That would work. The one I built can mill down to 1/4" thick.