WizardOfBoz

Looks like phenolic laminate plywood. I'd love to have a piece of this: I want to put me trying stand on something like an 18 x 24" sheet of this, with rubber feet on the bottom.

If you do use the Stainless sheet for a wear-pad under your stand, I'd mount the stand into the concrete unless the stainless is pretty thick (better than 1/8 inch, or about 11 gauge or better). If you mount your stand to the plate, and you want the bolts going up through the bottom using countersunk head bolts, and your metal is that thick, you can countersink it. If you try this with thinner sheet (0.040 or so, or less) then I suggest dimpling your countersinks, not drilling them. If you drill a countersink into thin sheet, you make it even thinner. If you drill your hole undersize initally, and use a dimpling die to bend the countersink into the sheet, you have a stronger bond. The orthodox way to do this is to use dies and a press. I suspect that you could take a piece of pipe and chamfer its id at the end, and pound a high quality steel countersunk bolt through the hole in into the chamferred pipe and you could achieve the same thing. Dies and diagram below.