Assuming you will fix the hole with a BSW 5/16-18 coil, you could try using an 8mm screw temporarily. The 8mm screw will be just 0.025" bigger than the 5/16 screw. Maybe, hack-saw a length-wise slot through the 8mm threads to act sort of like a tap cutting edge. The drill in a BSW 5/16-18 coil kit is 8.3 mm, so this bodge should not bother your future repair. I don't guarantee this will work, but if it were my problem, I'd try it.
Richard L.