The metal I'm most used to working with is the soft aluminum flat
bar from the local hardware Borg.

Using a 1/8" (thick) x 3/4" (wide) x 3" (long) piece of that soft
aluminum. Make a U shape out of it. If that U shaped piece of
aluminum flat bar is turned upside down and the ends glued to a hard
surface, I know approximately how much weight I could put on it
before it buckled.

What would be the equivalent approximate thickness of 301/304
stainless steel to 1/8" thick soft aluminum flat bar? Any idea will
help.

Thanks.