Without disassembly to check the vertical 2"x2" is attached to the 1/2"x2" with wood glue and drywall screws and then attached to the bench with drywall screws. I drilled a hole for the stem and then the clamping screw and tapped the clamp screw hole with a 1/4" tap. Dried oak taps really well, no one ever taught me better than do it. You can drill a hole in pine or softer wood, fill it with epoxy, redrill and then tap, works very well.
It you find a crew installed iron water mains, they will probably give you oak 4X4's. Around here they typically bury them, they are rough sawed and sometime have splits but you can get some very workable wood out of them.