How to measure thread





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  1. #1
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    Default How to measure thread

    Hi all.

    How do you measure thread without a thread gauge.
    Can you record the bolts outside diameter and just count the amount of thread in a certain distance?

  2. #2
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    You can measure OD (Outer diameter) and the threads per inch.

    Also remember length (obvious) but thread length as well.

    Check the head for the grade ie. 8.8
    Everything is a hammer.
    Unless it is a screw driver.

    Then it it a chisel.

  3. #3
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    Ja. I've always wondered about those numbers on the head of a bolt. What do they mean? I thought it was shear strength or something to do with the composition of the metal.

  4. #4
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    It indicates the strength of the bolt. The first digit is the Ultimate tensile strength (UTS). the second is the yield strength.

    So if you have a grade 8.8 bolt, the UTS is 800MPa, and the Yield is 80% of that, ie, 640 MPa.

    On a 10.9 bolt, the UTS is 1000 MPa, and yield is 90% of that, ie 900 MPa (IOW, a bloody strong bolt).
    Last edited by Uys; 2011/08/22 at 09:02 AM.
    Everything is a hammer.
    Unless it is a screw driver.

    Then it it a chisel.

  5. #5
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    Thanks Uys!

  6. #6
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    Ok.

    I have a 8.8 bolt with an od of 16mm and 10threads per inch so....
    If i want thread cut on a shaft i can ask for 10threads per inch on a M16 bolt, would this be correct?

  7. #7
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    Ok, so you have a 2.5 pitch (25.4/10). M16 standard (most commonly used is M16x2, so you have a coarse thread bolt. You can ask for M16 x 2.5
    Everything is a hammer.
    Unless it is a screw driver.

    Then it it a chisel.

  8. #8
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    Thanx Uys.

    I need bolts made for my new shackles (as they are a bit thicker than the standard) and didnt know what to ask for @ the Ingeneering works.

    Aprecciate the help

  9. #9
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    Why made? Why don't you just go and buy them?
    Everything is a hammer.
    Unless it is a screw driver.

    Then it it a chisel.

  10. #10
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    I did go to nuts & bolts but the bolt has no tread for 75mm (OD 16mm here it goes through the rubber in the leaf spring) then it has a step down to about OD14mm and has thread for about 20mm. If that makes sence.

  11. #11
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    Default Re: How to measure thread

    metric bolts are not measured per inch. Measure 10 threads in mm and divide by 10 to get the pich.

  12. #12
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    Default Re: How to measure thread

    Problem making bolts is the heat treatment. Up to a reasonable size 8.8 bolts are made out of ancient material EN8. When it sold it is hot rolled and I would not use this material in that condition. Last Sunday I rejected design where it was done. After machining material is quenched and tempered. There is a diameter limit after which EN8 is no good. It either cracks or sufficient strength is not achieved. To solve this we used to specify EN19, which is an other ancient material. To eliminate all these heat treatment issues I normally specify for heavily loaded rods ASTM A193 B7. It is readily available as threaded bar.

    You can always make bolts out of mild steel but is such strong enough is an issue.

    Easy way out might be to buy over sized or correct size 8.8 bolts and give those for machining. B7 is available in M16.
    Jouko
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    Never drive a normal car 8)

  13. #13
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    Default Re: How to measure thread

    Quote Originally Posted by Jaco L View Post
    I did go to nuts & bolts but the bolt has no tread for 75mm (OD 16mm here it goes through the rubber in the leaf spring) then it has a step down to about OD14mm and has thread for about 20mm. If that makes sence.
    My Hardbody had shackle bolts like that. (with the step)

    Any "spring works" shop should have them on the shelf.

    The bolt should come with matching nuts.
    Last edited by KobusDJ; 2019/08/15 at 07:49 PM.
    Kobus

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  14. #14
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    Default Re: How to measure thread

    Is this what you are looking for?



    It is a shoulder bolt. 16mm. It step down to 12mm (threaded). The step is there to prevent overtightening . You don't want to pinch the spring eye between the 2 plates. It needs free movement to do its job.



    The shackle bolt/pin should NOT have free rotational movement. (See what they did in the pictures). The only movement should be the spring eye on the bushes (that is their job). Sometimes the bolts gets manufactured (pressed/welded) to the plate on one side.
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    Kobus

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