Reply to "Ring bolt ? again."

shearing off bolt heads leads me to believe you have a loose fitting housing set. a clean shear is a sign of possibly too hard of bolt (if there is such a thing)or too much torque at assy. if the heads are leaving a witness mark on the carrier then they are working. this is not to say the carrier is too hard for the bolts to hold. just the wrong application. I would stay with a grade 8 or Grade 9 standard style head and safety wire. grade 12 may be too brittle and cause the same problem. it has no elasticity. a short shoulder on the bolt never hurts and helps take up any slop in the holes. you may consider drilling additional holes and dowel pin it, peening the holes at the open ends of course.