As an old fabricator and welder I can assure you that SS is NOT stronger than most common steels. There are tool steels that are much harder but they are not what goes into an engine. Typical stainless steel is less than a grade 5 bolt woud be. I do agree about the use of hardware store fasteners because so much of the ones they carry are Indian and Chinese imports and little if any quality control.
As Grigg stated there are MANY different SS alloys. I used to run into that constantly on sheet steel with 304 vs 409.
Bolts are the same way, know what you are buying.
