Helicoil...here is a link:
http://www.helicoil.in/helicoil.htm
You can also:
1. Drill & tap to next larger size...cut and weld new threaded end on ball stud to fit new hole size.
2. Infill the hole with a TIG weld, drill and tap to original size.
3. Use some of the epoxy compounds on the ball stud, to securely fasten it into the factory threaded hole in the block.
Good luck and let us know how things turn out.