You could always drill out the holes and move up to a 9/16 fine thread US Grade 8 bolt. That would be closer to 14mm diameter. If you're worried about pull out on the threads, double nut it! <img src="/forums/images/graemlins/kewl.gif" alt="" /> that should net more overall pull out strength then the single fine thread nut.

-Todd
1987 Montero 2.6l 5-speed (Sold...but I still miss her)
2008 Jeep Patriot Sport 4x4