Is there any way to grip the nut on the other side with some pliers? Maybe needle nose pliers could get ahold of it.
Other than that, you could buy some 2-part epoxy or another good glue, and dab a bit in between the part that's spinning and the mask (make sure you don't fuse the screw to the nut though
), let it dry so that it can't spin anymore, and then tighten it down.
Other than that, you could buy some 2-part epoxy or another good glue, and dab a bit in between the part that's spinning and the mask (make sure you don't fuse the screw to the nut though