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Thread: M bolt sizes to Allen/hex key.

  1. #1
    Join Date: Oct 2011

    Location: Bacup

    Posts: 458
    I'm Andrew.

    Default M bolt sizes to Allen/hex key.

    I wonder if someone can help me find the correct size replacement bolt/screws. I am using my Allen keys to try to find the correct size bolts but the conversion charts are either contradictory or at least confusing. I wonder if someone can point me to a chart or give me the right sizes. Bolt one is a socket head and the Allen key that fits is a 2.5 mm. Bolt two is countersunk and a 2 mm key fits. I get them both to be M3. It is confusing that the M size changes with the head type. Am I correct? Thanks in advance. Andy.

  2. #2
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 5,128
    I'm Alan.

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    It is confusing, best to measure the thread diameter of the bolt, it will be close to 3mm or 2.5mm.

  3. #3
    Join Date: Oct 2011

    Location: Bacup

    Posts: 458
    I'm Andrew.

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    Thanks Alan. I'm not sure my eyesight is up to that! and I don't have a micrometer. I'll have a bash.

  4. #4
    Join Date: Nov 2008

    Location: Valley of the Hazels

    Posts: 8,942
    I'm AMusicFanNotAnAudiophile.

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    Chris



    Common sense isn't anymore!

  5. #5
    Join Date: Oct 2011

    Location: Bacup

    Posts: 458
    I'm Andrew.

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    As an example of the confusion. I have bolts that I know are M2 and according to the charts should take a 1.5mm Allen key but actually only take 1.3 mm. It's a good job I'm not building something serious like a plane or a nuclear reactor!

  6. #6
    Join Date: Oct 2011

    Location: Bacup

    Posts: 458
    I'm Andrew.

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    Brilliant, thanks Chris. I think that chart confirms what I thought. Andy.

  7. #7
    Join Date: Dec 2018

    Location: Cambridgeshire UK

    Posts: 28
    I'm William.

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    Hi

    One of the easiest ways I ‘ve Is if possible go take the bolts into somewhere like B&Q and try to find a nut that fits.

    Hope it helps

  8. #8
    Join Date: Oct 2011

    Location: Bacup

    Posts: 458
    I'm Andrew.

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    Thanks William. I'ts only a couple of quids worth so I'm taking a punt on ebay. Andy.

  9. #9
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 3,311
    I'm Lawrence.

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    Quote Originally Posted by RMutt View Post
    As an example of the confusion. I have bolts that I know are M2 and according to the charts should take a 1.5mm Allen key but actually only take 1.3 mm. It's a good job I'm not building something serious like a plane or a nuclear reactor!
    Even then they mix up metric and imperial and still mess them up can't remember the famous case maybe someone here knows

    Sent from my POT-LX1 using Tapatalk

  10. #10
    Join Date: Oct 2011

    Location: Bacup

    Posts: 458
    I'm Andrew.

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    Quote Originally Posted by Lawrence001 View Post
    Even then they mix up metric and imperial and still mess them up can't remember the famous case maybe someone here knows

    Sent from my POT-LX1 using Tapatalk
    A couple here Lawrence.
    https://www.simscale.com/blog/2017/1...rbiter-metric/
    https://www.bbc.co.uk/news/magazine-27509559

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