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Metric vs SAE

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  • Metric vs SAE

    I ran in to something today that was interesting I'm building a roller track for a customer. And the rollers I bought have weird thread 11-1.25mm as stated on a small greasy piece of paper in the box. So I ordered a tap from Enco. came the next day. So today I figured out a tap drill 9.8mm that works out to approx .386" the tap drill for a 7/16x20 tap is a size W which is .386.
    This caused me to go HMMMMM!
    So I grabbed a 7/16x20 nut and it screwed right on the metric thread of the roller. The OD is the same and it's hard to tell which is which with a thread Gauge.

    So a 11-1.25mm and a 7/16x20 seam to be interchangeable


  • #2
    If the threads have a loose tolerance, they may interchange,

    but translating M11 - 1.25 to inches gives 0.433" X 20.32TPI

    or the other way around,

    5/16 X 20 becomes M11.1125 - 1.27

    So the interchange in not perfect. The metric OD is smaller by only 0.0045" so the metric nut would work on almost all 7/16" threads, but the English nut may lack the necessary strength on a metric screw and may fail.

    It has been pointed out that several metric threads have "almost" equilivants in the English system and of course, vise-versa. But it is probably not good practice to interchange them.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!