I don’t have any data on stainless steel bolts which are especially great for body attachments, etc…But I have often heard that they were more brittle than other bolts…anybody have info on using them especially in undercarriage work, steering, suspension …critical stuff.
I destroyed a stainless steel bolt recently with just a wrench and a ratchet. Really surprised me how easily it failed. I was replacing a rusted failed bolt on the exhaust connection between the 2 cats on the right side. Bolt was maybe 1/4in or so and just snapped in half when I tightened it too much. Next bolt I was more gentle with but then again you want well-sealed exhaust joints so I may reevaluate that bolt in that place. At least that’s a very easy spot to get to (unlike so many others) on this car!
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Dave, the only time I will use stainless bolts is when I want to “dress-up” an engine. They polish very nicely. Never anything critical. Grade 5 or 8 for that.
I thought so…ok for hanging the license plate or something like that…have seen other stainless stuff get stress cracks from overuse
There is 300 series and 400 series stainless. Anyone know which one most SS bolts are made from?
I have long considered stainless bolts to be roughly equal to Grade 5 in strength. They have the nice feature, though, that they don’t lose strength due to rust.
IMHO, bridges should use stainless steel for all structural steel. Hear me out. When you build a bridge using regular steel, you’ve got to paint it, so you’ve got to include the cost of painting in your comparison. But after you’ve built the bridge, you have to have a qualified inspector thoroughly inspect the bridge periodically to keep an eye on the corrosion issues. So you also need to factor in the cost of all those inspections, plus any repairs that are required. And eventually, you’re going to have to close the bridge and tear it down before it falls down and hurts somebody. So your life cycle cost of having a bridge includes the cost of a complete replacement every 75 years or so.
Meanwhile, if you use stainless steel for the structure, you build it and forget it. Maybe come back in 100 years and confirm it’s still good as new. It’ll probably last 1000 years, maybe more.
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Have you got a cast iron guarantee on that stain-less steel? I’ve just had to return a kettle to Amazon because it has developed a rust spot that is not just on the surface.
Most stainless bolts you see are 18-8 stainless, which is a grade of 304. 316 stainless is generally found in the chemical process industry and saltwater marine use.
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You can learn a great deal about threaded fasteners, their strength and appropriate materials on ARP and McMaster-Carr websites. If you need aviation grade, Aircraft Spruce is a good hobbyist source.
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Back in my race car days, AS was one of my favorite Department stores…
Remember: you got a catalog from them, called them, they sent you stuff, then you sent them a check.
Really not sure how I ran a bidness, W/O the Interwebz…
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Back when they actually still sold airframe grade spruce! 
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I’m a retired registered mechanical engineer (PE) who spent his career in chemical plants and distilleries. For non load bearing structures, or structures in extreme environments (chloride, high temperatures) your approach is valid. I used to spec stainless boiler stacks (combustion gasses are hot and acidic) because it cost no more than a property coated carbon steel unit. But for your example, bridges, load bearing structural applications, stainless is not strong enough to complete with steel alloys. Not only is it more expensive $/ton, it would take MANY more tons of stainless. You are ignoring the railroad bridge alternative. They use a grade of steel they know will rust but they overbuild it to such a degree that they know it will last a hundred years, unpainted.
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Stop it! I do not need another hobby! 
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I like using the yellow zinc plated grade8 steel bolts, etc. Won’t last as long as stainless, but should not corrode during the 10-20 year life it will serve until I need to take it apart again.
by far the best fasteners I ever used…was told they were SS exhaust manifold bolts made by Caterpillar
they attached the down pipes on a 4wd I bought, had 12 point heads, and were a dark grey color, dull not shiny
I had that vehicle over 10 years and had the exhaust down a few times.
The fasteners never showed the slightest amount of galling or discolouration
I tried to buy some, but was told by the fasteners specialists they were not available to the public, and had probably been pinched of a worksite (PO worked in an open cut coal mine)
good point…fastener specialist was saying he couldnt get them
more than likely, if I had a part num, it would have been possible to obtain them from Cat
before I forget…thanks to @PeterCrespin, who espoused allen-head fasteners
I used SS allen-heads on my custom SS exhaust, and it made adjustment a breeze, improving the previous arrangement which was very awkward
Funny story, provided you aren’t my Belgian cousin Erik…
Rust is good sometimes.
Erik is a engineer perfectionist and a shipping salvage/recovery assessor. That’s shipping as in Europe - using ships.
The Dutch/Belgians are world leaders and they are called in for major incidents worldwide. Not much Erik doesn’t know about steels and corrosion.
So Erik constructs a wooden deck in his suburban Antwerp home. What’s he gonna use for nails in damp Northern Europe? Stainless nails in beautiful light wood. No rows of rust blemishes for Erik, no siree! No rest, either…
The nails are so slick they gradually work up after so many hot/cold, wet/dry and expand/shrink cycles. Every so often he has to go round and tap the buggers down again.
His middle name should be Sysiphus.
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Indeed: why old-time carpenters would chuck new nails out in pans, and let them get good and rusty, before use.
I threw away all my nails years ago. To assemble decking properly involves SS deck screws:
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