Were those grade 8 stainless? I've never had a problem with running a regular grade 8 bolt in these. Some shoulder would help as it swells up a little in that area and would act as a shoulder. I would ask someone like Garner-Wescott or Stainless Specialities for a catalog or go on line and look for ones that have as much shoulder as possible. And, I would use Nylock nuts with them for sure.

Don