The bolts are 6mm Metric some are Allen / Torx mostly though have a 10mm across flats bolt head, about 25mm long.
Sometimes you can get away with a longer bolt to catch the undamaged thread. When I was faced with this, I wrapped the bolt with electrical tape & forced it in, intending to do a proper repair in daylight, Lasted 3 years
There have been posts on this subject:-
Proper repair, A helicoil (threaded insert).
Clean hole, fill with Chemical metal, allow to harden, drill & tap.
Clean hole, lightly grease bolt, fill hole with araldite or similar, push in bolt, jiggling to ensure glue flows into gaps, allow to set, remove bolt, as the grease stopped the glue from sticking to it.
As above but glue (without grease) studding into hole, fit
, then put a 6mm nut on.
HTH Tim, Bodger extroadinaire.