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Thread: Understanding machine screw sizes

  1. #21
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    Thanks for all the information. I knew there had to be some sort of formula for figuring this out, just like they have a formula figuring out rebar sizes.



    -JW:

  2. #22
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    Dec 2012
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    Quote Originally Posted by Bented View Post
    The major diameter of a numbered machine screw in the US system is:
    The size number X .013" + .060".....Even more inexplicable is the fact that someone devised a system of screw sizing using this formula 100 years ago.
    You think the present system is bad?

    Prior to 1908, the standard was, Nominal Major Diameter = 0.05784 + (.01316* the size number).

    SO a #10 screw had a diameter of 0.18944 instead of the current 0.19000, etc.

    Starting in 1908, the ASME had a committee working on changing the standard-they issued reports in 1908, 1917 & 1920, and the new system was finally adopted in 1920.

  3. #23
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    Thanks Andy.
    I always appreciate historical information like this.

    -D
    DZER

  4. #24
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    It was much later than that before SAE got involved. Many of the early cars had all manner of sizes. Most produced right in the car factory to fit a specific part. This included special bolt head sizes and shapes.

  5. #25
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    Quote Originally Posted by Bented View Post
    The major diameter of a numbered machine screw in the US system is:
    The size number X .013" + .060"

    Therefore a #4 screw has a Maj. Dia. of .112" maximum.

    I do not know why I have remembered this for 30 years, it is inexplicable.

    ....
    I bet you have remembered it for the same reason I have: it was such an eye-opening revelation ...a forehead slapping moment. A piece of info that's handy to know.

  6. #26
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    Oct 2013
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    I have usually used the following for clearance holes:

    Size - Fraction - Decimal - Clearance
    #4 --- 1/8" ----- 0.125" -- 0.013"
    #6 --- 5/32" ---- 0.156" -- 0.018"
    #8 --- 3/16" ---- 0.187" -- 0.023"
    #10a - 13/64" --- 0.203" -- 0.013" (close fit)
    #10 -- 7/32" ---- 0.219" -- 0.029"

    That made it easy to use common fractional drill sizes, and easy to remember. Also, they give between 12% and 15% clearance.

  7. #27

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    Quote Originally Posted by lynnl View Post
    I bet you have remembered it for the same reason I have: it was such an eye-opening revelation ...a forehead slapping moment. A piece of info that's handy to know.
    I think that I was just young and could remember useless knowledge at the time (-:

  8. #28
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    Jul 2017
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    Buffalo NY USA
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    Quote Originally Posted by andywander View Post
    You think the present system is bad?

    Prior to 1908, the standard was, Nominal Major Diameter = 0.05784 + (.01316* the size number).

    SO a #10 screw had a diameter of 0.18944 instead of the current 0.19000, etc.

    Starting in 1908, the ASME had a committee working on changing the standard-they issued reports in 1908, 1917 & 1920, and the new system was finally adopted in 1920.
    X2 Thanks, historical information is invaluable. I'm trying to get a time frame for some of my taps and dies, thanks again.

  9. #29

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    Quote Originally Posted by CCWKen View Post
    It was much later than that before SAE got involved. Many of the early cars had all manner of sizes. Most produced right in the car factory to fit a specific part. This included special bolt head sizes and shapes.
    ASTM has a broader range of ASTM standard threads then the SAE.

    However this does not preclude anyone from making any thread combination that they desire, you simply can not claim that they are ASTM/SAE standard dimensions. Because I am not a particularly nice person I have made mating threaded parts that have very proprietary thread dimensions simply to confuse people in the future (-:

    I once made some dedicated gear pullers for a repair company, the threads were 1 1/4-15 11/16 threads per inch, they never figured that out.

  10. #30
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    Mar 2015
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    F it, I'll just use metric hardware!

    Sent from my SM-G950U1 using Tapatalk

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