Nuts and bolts

Discussion in 'General maintenance, upgrades and modifications' started by svvg, May 2, 2020.

  1. 2 May 2020 at 10:45 AM #1
    svvg

    svvg Achieved official socks

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    Hi all. Whenever I work on the bmws or vws in our family I tend to replace relevant fixings with bmw or vw parts where required, as it’s easy to identify part numbers, and I’ve usually researched the parts/diagrams and how to effect a repair before doing so - and all the cars I have are pretty old, so new nuts and bolts which I know will fit and be strong enough for the purpose has been the way forwards for me (a lot of suspension bits come with new nuts anyway....).

    However - I know it’s not necessary to use bmw/vw bits - and I also have an older pug track car I work on - but have no idea what quality of bolt I should use if I decide to buy independently. There are hundreds of suppliers on ebay and I have thread size and pitch gauges, but I have no idea what quality or rating of steel I should be buying. I've seen references to grade 5, 8.8 and 10. But haven't got a clue what I should buy.

    Please could someone shed some light on this?

    Many thanks,

    Svvg
     
  2. 10 May 2020 at 8:30 PM #2
    TATI

    TATI On the path

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    Hi

    this denotes tensile strength of bolts - the higher the number the higher the tensile load, if you have a A2 for example this is the quality of the thread noramlly come as A2 or A4

    Head Markings
    Metric Bolt Class
    Mechanical Properties

    Proof Load (MPa)

    Min Yield (MPa)

    Min Tensile Strength (MPa)

    [​IMG]
    Class 8.8

    Medium carbon steel, quenched and tempered

    580-600

    640-660

    800-830

    [​IMG]
    Class 10.9

    Alloy Steel, quenched and tempered

    830

    940

    1040

    [​IMG]
    Class 12.9

    Alloy Steel, quenched and tempered

    970

    1100

    1220

    [​IMG]
    A2 Stainless

    Also called 18-8 or type 304 stainless steel*

    N/A

    210 Min.

    450 Typical

    500 Min.

    700 Typical

    Proof Load: An axial tensile load which the product must withstand without evidence of any permanent set.

    Yield Strength: The maximum load at which a material exhibits a specific permanent deformation

    1MPa = 1N/mm2 = 145 pounds/inch2

    Tensile Strength: The maximum load in tension (pulling apart) which a material can withstand before breaking or fracturing.

    * Stainless markings often vary, though commonly stamped A-2. Most stainless is non-magnetic, though 410 Hardened stainless is ALWAYS magnetic.
     
  3. 10 May 2020 at 9:20 PM #3
    mid lid

    mid lid Rocking a new hat

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    Most suspension fixings will be grade 8.8, high stress components like flywheels/brake fixings are sometimes 10.9. Grade 12.9 fixings are rarer but still used in certain applications.

    Don't use stainless steel fixings on anything with a specified torque setting and when using stainless for cosmetic fixings then you need to use a suitable grease to prevent dissimilar metals corrosion.

    The best thing to do if the existing fixings are too corroded to read the grade from is to get hold of manufactures parts lookup software as this usually gives you the bolt specifications.

    This is what I do and I use this site to get them from:

    https://www.westfieldfasteners.co.uk/
     
  4. 10 May 2020 at 11:30 PM #4
    svvg

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    Thanks very much for the above. Didn’t realise stainless could have issues with torquing, so that’s good to know. Looks like grade 8.8 for most stuff - unless it could kill you if it broke - so grade 10.9? Assume there’s no harm, save for price, in going for 10.9 of it’s available for everything?
     
  5. 11 May 2020 at 7:49 AM #5
    mid lid

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    Yea for a track car its probably a safe bet to go for 10.9 if you cant find the recommended specs.

    The issue with stainless bolts isn't so much in the torquing but in the behaviour of the bolt under stress compared with regular steel, but a good rule to follow imo as it keeps you from using them on anything critical
     
  6. 11 May 2020 at 9:17 AM #6
    svvg

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    Thanks for this. Much appreciated, and makes sense/filled the gaps in my potted understanding of the numbers on bolts etc(!).
     

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