What's the shear strength of M3-M10 304 stainless bolts?

Discussion in 'The Garage' started by MauiCowie, Aug 12, 2020.

  1. MauiCowie

    MauiCowie Long timer

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    I'm a slut for replacing hardware on my bikes with stainless hardware because I'm a crow and like shiny stuff. Having an undergrad degree in engineering I spent a fair amount of time studying materials science so I'm a kind of a nerd and interested in the comparative strength of various materials.

    Out of curiosity I thought that a quick Google would let me know what the shear strength of M3, M4, M5, M6, M8 and M10 304 stainless bolts is. I could not have been more wrong. What I was looking for was a simple table but all I could find was exasperatingly long descriptions of chemical composition and yada, yada, yada . . .

    All that I really wanted was ballpark figures on the shear strength of these bolts and how it compares to, say, 8.8 steel bolts.
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  2. Bigger Al

    Bigger Al Still a stupid tire guy Supporter

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    You also need to consider the effects of stainless steel vs. the material that you are putting it into. My personal experience is that stainless tends to seize and gall when used in aluminum, even when anti-seize compound is employed.

    Your best bet for strength info is to contact a manufacturer of hardware and see if they can get you a chart.
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  3. dtysdalx2

    dtysdalx2 Only a matter of time.

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  4. theDoktor

    theDoktor Husky Racer

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    Let me throw you another curve ball in your knowledge quest: are you looking for single shear or double-shear values?
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  5. Coma

    Coma Long timer Supporter

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    And what is your shear axis?
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  6. tomrux

    tomrux Long timer

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    Huh ? Shear is shear. Anything not at 90 degrees to the fastner longitudinal axis is not going to be true shearing force but a combination of different forces.

    Cheers
    Tom R
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  7. nickguzzi

    nickguzzi Long timer

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    I bought the guzzi 40 years ago for everyday and long touring holiday use.
    Italian bikes of the era had a preputation for rusting faasteners. So everything not critical got replaced with stainless. And copaslip.
    All the gearbox fasteners. All the valve and front cover fasteners. I particular the engine mount bolts. All guards/fenders. Everything handlebar and lights fittings. Exhaust became stainless too - and all the fittings, including into the head.
    None - not one - has ever galled or seized.
    At the time I was visiting Ireland frequently, you don't know the meaning of road slime until you have ridden around there for a while. Riding around everyday, winter and summer in the UK, a place not known for dry weather, and cold enough for snow, and therefore salt.
    I have never been accused of washing my bikes with any regularity either.

    Common sense - no power tools. Antiseize. And initially at least, careful checking

    Pretty much any fastener supplier will have an online chart of bolt tensile strengths.
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  8. Coma

    Coma Long timer Supporter

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    Doh! Tensile strength and yield was what was in my head. Materials classes were 4 decade ago.

    What I did find was that shear strength in bolts is not defined by ATSM. Rule of thumb puts it at ~60% of tensile.

    “First, unlike tensile and yield strengths, there are no published shear strength values or requirements for ASTM specifications. The Industrial Fastener Institute (Inch Fastener Standards, 7th ed. 2003. B-8) states that shear strength is approximately 60% of the minimum tensile strength.”

    https://www.portlandbolt.com/technical/faqs/bolt-shear-strength-considerations/
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  9. Zoef zoef

    Zoef zoef Long timer

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    304 is significantly weaker than 8.8, about one third. If you want to replace 8.8 with stainless steel, you should look at A4-80, which is somewhat comparable. There are some iffs and butts to be aware of. One being galling.
    #9
  10. Beezer

    Beezer Long timer Supporter

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    whats the airspeed of an unladened sparrow....
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  11. bwringer

    bwringer Gimpy, Yet Alacritous

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    I also like shiny things, but I never use stainless where it's under a lot of load. Stainless, at least the variety us mortals can obtain at reasonable cost, can be brittle.

    For example, footpeg, brake, or handlebar fasteners. I have replaced these with high grade (12.9) zinc-coated fasteners, but not stainless.
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  12. Zoef zoef

    Zoef zoef Long timer

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    Hmmm, 12.9 bolts are known to be brittle too. Maximum, without becoming too brittle, is 10.9 (in general).
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  13. dhally

    dhally Hammerhead Supporter

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    Dusting off my brain, if the screw is torqued down you won't have pure shear loading. There will be axial loading AND shear, with maximum stress occurring at an angle. Vectors are involved in the solution IIRC. Need to dust off your machine design text.
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  14. Zuber

    Zuber Zoob Supporter

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    If you want bling and strength, take your high strength bolts to a platter and have them nickle plated. Not chrome shiny, but a nice metal surface.
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  15. eakins

    eakins Butler Maps

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    Zinc 10.9 flanges have become my favorite bolts. Rust proof, nice wide head, strong, never strips out like socket/hex/allen bolts can.

    I was a fan a stainless button nose bolts for years but that are just soft cheese in reality.
    I'll buy 12.9 zinc buttons now if I really need a smooth bolt head.


    10.9 zinc flanges:
    Well stocked at Ace or
    https://www.boltdepot.com/Metric_flange_bolts.aspx
    #15
  16. eakins

    eakins Butler Maps

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