My dad bought the one I have back when they only made one model. Early to mid 70's maybe? Anyway the jaws are Baltic Birch-looking, high ply count plywood. Marine ply maybe? I hand sanded them and re-topped them with poly a decade or so ago. Still going strong. I imagine anything stout that would survive where you plan to use them would be fine. Ash is pretty tough, pecan is harder than all get out. White oak would take moisture abuse but, then again, so would marine ply.
Any sufficiently advanced technology is indistinguishable from magic.
- Arthur C. Clarke