Hey 9od, are we talking about east/west bars, or north/south (vertical).
Vertically, round bar tends to jamb just a bit more than flat bar.
3 or 5mm x 12mm alloy flat bar will keep the weight down.
I prefer to use Stainless steel punch sheet.
Strong once a lip is is folded on each side.
You want high percentage punch. ( lot of holes psm)
I can source at a decent rate if needed.
There is a preferable side to use on this stuff....
One has a dimple from punch process.
The other side is flat and is not deformed with dimples
Use this side up.
Less jambing occurs.
Remember there is no rule that a classifier has to be parallel to the base of the hopper.