The theory, as explained to me in reference to boat maintenance, is that electrons will attempt to escape to the water, and using a metal, like zinc, that lets go of them faster, will prevent more "noble" metals from corroding.....
But, I think the zincs will corrode away regardless of being connected to another metal. Maybe a little faster? But those stainless screws aren't going to be large enough to make that kinda difference. If those captive nuts are in a corrosive environment, the entire steel body is going to rust. (If you had a fiberglass or aluminum body, you'd want to put a bit more thought into it.)
So, I use them. I'm going to use either stainless or zinc plated, not bare uncoated carbon steel.
They are not as strong, as
@Bear mentioned. I'm sure they are fine holding the radiator in, front bib to the fenders, transmission tunnel to the tub, but I'm not using them on suspension, roll cage, seats and seat belts, or anything in the drive train (maybe to hold the rear axle inspection cover on?).
And, I've also been told they don't conduct electricity as well. (saw someone in a boat melt their battery post using stainless nuts and washers to attach the cable). So, you probably need to be careful using them anywhere that you might need things to ground (windshield hinges?).
The one place I used them that I'm still questioning is the thermostat housing. Those two M10 ( or M8?) bolts that never just unscrew and always seem more rusted than anything else. And I did use anti seize on them. Gimme a couple years, or so, or however long the thermostat and everything else lasts and maybe I'll remember to report back....
