Originally Posted by
JDNSW
The effect is not that simple - but probably worse is that most stainless steels will work harden and crack with vibration or cyclic loading. To amplify the original "Just don't replace any on anything that requires a high tensile bolt" - don't replace anything where failure of the fastener would be critical.
Stainless is no worse than mild steel in setting up a galvanic cell to corrode aluminium, the difference is that the stainless makes better contact unless precautions are taken as it has no paint or oxide layer. Galvanised or, better, sherardised (not zinc plated) fasteners last nearly as long in most conditions and the zinc protects the aluminium close to it as well - e.g. galvanised cappings on older Landrovers. (Galvanised bolts and nuts are hard to find these days and sherardised ones almost impossible)
John