Has anyone been able to figure out how to remove the long center tie-down bolt that holds the jack in the tray under the rear seat of an extended cab?

There is a bolt on the in-board side that is easy to remove, but the other one is the long one that is a threaded rod that extends up high to hold down the jack with a wing nut. I could not see any nut under the vehicle at that point so I do not understand what holds it down.

It has a tiny little hex head that strips out easily, and visegrips on the shaft turn it a little, but not enough to unscrew anything.