clifto wrote:
I have a heavy-duty massager whose main structure is held together by two
pieces of threaded rod about 3" long. The rods are partially stripped at
the ends; nuts need to be turned to put them on, but they're quite loose. It
doesn't look like it would be possible for me to replace the rods, so I'm
wondering if there's any sane and relatively permanent way to repair the
threads. Whatever I use has to tolerate a LOT of vibration, of course.

A new nut may solve the problem.
If a new nut also slides then re thread the rod with the next smaller die and get a
nut to fit that new size.