OBM says that all of it is just A36 mild steel unless they're using an alloy steel.
Mine are diamond plate, tough as nails. I use them to pivot on rocks and have landed HARD on them and have only scraped the paint off.
You will prolly have trouble getting diamond plate unless you have something custom built.
Here are some really goods ones by Shrockworks
. They offer good protection all the way under like mine do.
The diamond plate looks nice on the factory Rubicon rocker guards, but believe me when I say, it can get old after awhile. I sometimes wish that mine were flat instead of diamond plate because they don't match anything.
Kinda hard to see, but you get the idea.