I'm not sure what comes in the "packs" sold by Totally Stainless, but they do sell 17-4PH fasteners, which are much stronger than 303/304, and should be used on joints where safety is important. McMaster-Carr also sells 17-4PH fasteners - much more expensive than Totally Stainless, but they can come with a "pedigree", if that is important. It certainly is in the aircraft industry.
