David, Not exactly sure what you are wanting to do...one thing that comes to mind may be that the caged nuts are spinning inside the cab mount so you want to drill holes in the floor & work on them from the top? To give an answer to how thick...it depends on where your talking. Above the cab mount is a couple layers, but it's not an 1/8". I've never seen holesaws rated to a depth, not saying they aren't...just not something I'm familiar with. What works best is a big, slow drill & either PB blaster, WD40 or even water to cool the cutter while your going at it. heat KILLS holesaws! I wouldn't sweat the thickness much as I've cut holes in 1/2" thick plate with normal holesaws. Good Luck, Lorne