Tony did a good job of explaining the differences. Let me add some more about stainless bolts and their use. I've had a "few" years of experience with airframe corrosion repair and design.
Biggest problem with stainless fasteners is thread galling. This occurs when you have a stainless nut on a stainless bolt. Under pressure, the threads will meld, making a joint that will not come apart. Put a big enough wrench on and you end up with a bolt that has threads stripped, but it's only where the nut was attached, meaning you have to cut either the nut or bolt to take it apart. To prevent thread galling you can use anti-sieze, a thread locker or a conventional steel nut, preferably cad-plated.
The next biggest issue is galvanic corrosion. This is where stainless steel is in contact with a non-ferrous metal, such as aluminum, copper or zinc. A small electrical field is created, causing both metals to corrode. Again, a barrier is needed. Anti-sieze, thread-locker, or wet paint.
Medium strength (blue) thread-locker is the preferred barrier, but it is expensive. Anti-sieze will wash out in exterior applications. Dipping a bolt in primer before assembly is messy at best.
If you buy stainless fasteners, avoid the Asian imports. Many are of unknown heat-treat and alloy. When I buy ss, I now only get made in the USA. A-R-P, Totally Stainless and Alloy Bolts are some good sources. Some of the truck parts vendors carry them.
