stainless screws

[richard]

Surely all of you have used stainless stuff a lot . just had a small parcel of , in my case , decorative screws . They came with the reminder " NOTE :- Stainless steel bolts should not be used in strength critical allocations (steering,brakes,suspension etc)" also the reminder that " it is good engineering practice to put a lubricant on stainless steel threads when fitting " - why is this and do we all do these things ?

[marcus]

I am no expert on stainless steel, but from what I know there are different grades of stainless steel, and many of them work harden, due to heat and/or "work". It could be that as some types harden they might also become brittle and fracture, whereas high tensile bolts tend to remain more stable re hardness and mechanical properties.

That said, I always thought that stainless steel were good for such use as mentioned, unless authenticity was required!

[Rusty Chrome (Malcolm Parker)]

Again, I'm no engineer but the long and the short of it is that it is possible to make a much stronger nut and bolt in carbon steel than is possible in stainless and stainless nuts and bolts are more prone to seizing, so if you plan on undoing them regularly or are using large sizes, you'll make life a lot easier for yourself if you use copper grease where possible. There are different grades of stainless steel fasteners available and anything that is vaguely strength critical go for the highest grade you can find. Most high strength bolt's from the 1950s are marked on the head.

Authenticity is fine as far as it goes, but unless you've got very deep pockets or are a talented machinist, progress on any restoration is going to be very slow indeed if you wish to source the correct strength bolt with the correct design head, length and finish in an imperial size.

Lots of interesting stuff on this site
http://www.boltscience.com/index.htm

http://www.roymech.co.uk/Useful_Tables/Screws/Strength.htm
http://www.qldcorvetteclub.com.au/tech/tech_talk/bolts.htm

[Bob Purton]

The advice I was given when I started restoring cars/bikes was if it is load bearing, use high tensile 8.8 .

[Big Al]

Normal Stainless Steel is brittle. Anyone who has had a stainless steel exhaust under mounting load will know that. It is a different material to steel and why it sounds different as an exhaust, normally noisier.
SS is in alloy so can be biased to suit certain tasks. You need to specify the task.

Fastners come in a range of specifications. I prefer to remain loyal to the original design unless its proved poor. Generally these people had better information than I do on specs needed. Its a pity that some spec fastners are not shiny or pretty but if you want prizes then you have the choice of putting the integrity of your machine into question. As a passing comment - insurance question
'Has your car been modified in any way?'
'Yes I decided that the original engineers used boring fastners so I changed them for some nice cheap shiny ones.'
How many folk return that to their insurer. Bit nasty when something falls off and causes an accident.

[Bob Purton]

Yes, agree with Al, A2-70 which all the usual fasteners are made from will snap under stress where as high tensile steel would bend rather than snap.   A2-80 is closer to 8.8 high tensile steel but why take a chance?