Ancient Chinese Secret [Linked Image]

When the screw fails to grab, wrap the screw with plumbers tape or even black tape if you do it tightly.... Put pressure on the screw when threading in to help the tape enter the screw hole... This is particularly useful with the old bakelite boxes that have a habit of cracking if a larger screw is introduced... Drywall screws seem to do well in PVC boxes that are stripped out...

-Randy