I mistakenly stripped the threads in either the bolt hole or the bolt itself and now it just spins freely. And I need to get it out so I can repair the threads. It is the bolt of the rear bumper and I don't have much space to work with and can't go behind it either. I also can't fit in a hacksaw to cut the head off. Any help would be appreciated.
Somehow moisture entered below the rear trunk from the outside to allow corrosion to occur. Rust. If the nut is spot welded onto a steel frame, the severe corrosion may have eroded the spot welds where the nut is no longer held in place. Sometimes pulling with just enough force with vise grips can force the spinning nut to wedge against the rusted frame enough to stop it from spinning to unscrew the bolt. Are you sure you can't see the nut from below where you might be able to grab the nut by hand or needle nose pliers or jam a screwdriver into holding the nut from spinning while someone uses a vise grip pulling and unscrewing the bolt?