These holes were dried oversized and tapped for oversized threads. The customers rail had come loose and the threads had been damaged beyond repair. Either drill out to the next size or drill for oversize. Drilling for oversize is the preferred fix.

Here we have the oversized screw being cutdown to fit flush with the bottom of the hole to provide the maximum holding power.

If you notice the last screw has a different head, this lets anyone know who removes this base in the future which screws go to the oversized holes and which one to the standard size.