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Can someone please help identify this grub screw type?

Discussion in 'Tools and Materials' started by devs, 13 Jun 2021.

  1. devs

    devs

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    Hi guys I’m looking to replace a failed hex grub screw and thought I’d bought a replacement. However the threads are different. Could someone let me know what type this is so that I can find online.

    correct one on right. B7C355A2-8216-4CFC-B64C-43C3C04C177B.png

    many thanks
     
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  3. Harry Bloomfield

    Harry Bloomfield

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    Find an ordinary machine screw which will fit the thread, then work it out from that.
     
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  4. mattylad

    mattylad

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    Without any dimensions to reference to its gonna be hard.

    I'll try 1/4" whitworth :)
     
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  5. devs

    devs

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    Thanks very much guys, I will track one down. Appreciated! :)
     
  6. just pumps

    just pumps

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    It is a coarse thread in the picture so could well be a whitworth thread, a clue to what it fits and age might help.
     
  7. JohnD

    JohnD

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    And its measurements, of course.
     
  8. JohnD

    JohnD

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    Or 1/8" or 3/16" or 1/2"

    Without measurements we will never know.
     
  9. JohnD

    JohnD

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    Hey, @devs

    Can you tell me what size nail this is, please?

    ae235.jpeg
     
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  11. just pumps

    just pumps

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  12. JohnD

    JohnD

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    it may look like that, but actually, it's very close


     
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  13. devs

    devs

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  14. devs

    devs

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    This is what I purchased that was incorrect...

    Screen Shot 2021-06-14 at 18.16.22.png
     
  15. JohnD

    JohnD

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    might be a UNC, since your original thread is quite clearly coarser.

    BSW is almost exactly the same as UNC (except in 1/2"), but not quite, so is not a precision fit.

    The "F" in UNF stands for "fine" (introduced for steel parts) and UNC is Coarse (intended for iron parts, like BSW) but also used into alloy castings.

    So 1/4" Whit or UNC will have a coarser thread, if that's what you need.

    knowing what device it fits, and what country it is made in, and when, would have given good leads.

    UNF and UNC if American, since about 1949, and still being used in a few primitive countries that resist SI units.

    Whitworth was introduced in UK in 1841

    Now mostly superceded by Metric in UK

    I think I can see about 5 threads on your 1/4" long old screw, so it is probably 20tpi, or maybe 24tpi if one has been chamfered off.

    1/4" BSW has 20tpi, so try that (or UNC, if it was made in USA since 1949, or in a country trading with the American market).

    There are 24tpi on 7⁄32" BSW which I think is probably not the one.

    There are some very strange anomalies, for example old Morris cars used metric threads but the bolts had imperial heads, since the engines were made by Hotchkiss but the Morris factory had Whitworth spanners.
     
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  16. devs

    devs

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    Wow what a wealth of knowledge. Many thanks for the detail. Appreciated! ;)
     
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  17. mattylad

    mattylad

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    What is the grub screw off?
     
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