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Thread: Seat belt/shoulder harness attach bolt size?

  1. #1
    supercub's Avatar
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    Apr 2002
    Let me check my GPS, gee how'd we ever navigate with those sectional things?
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    Seat belt/shoulder harness attach bolt size?

    What's the recommended bolt size to attach seat belts to the frame? I just bought new seat belt and shoulder harness's and the mount holes on the hardware are 3/8 inch. The mounts on the air frame are 5/16 inch. Should I make a bushing, or drill out the air frame fittings to 3/8 inch? What is typically done. Thanks

  2. #2
    wireweinie's Avatar
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    Aug 2013
    Palmer, AK
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    Normally have a small bushing that allows the seat belt triangle to swivel some. Each bushing should be slightly thicker than the piece it holds. And use a large enough washer under the head of the bolt to keep the triangle from slipping off.

    Also, think about welding a nut onto the back of the tab itself. This lets you install and remove the seat belts with just a socket wrench.

    Life's tough . . . wear a cup.
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  3. #3 mike mcs repair's Avatar
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    Aug 2004
    chugiak AK
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    small bolts are fine with a bushing...

    if you break the small bolt with your body in a crash, you won't be around anymore anyway.....

    Minimum tensile strength 125,000 PSI

    125000/16 * 5 = 39062.5 Lbs

    thats probably not the right math.. but you get the idea...

  4. #4
    Gordon Misch's Avatar
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    Dec 2003
    Toledo, Wa (KTDO)
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    For a 1/4" bolt - pi*.125^2 * 125,000 for double shear. Less than half that for simple shear because bending is also involved. I agree with Mike's conclusion - - -
    Last edited by Gordon Misch; 02-15-2020 at 11:17 AM.

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  5. #5

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    Jan 2017
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    I went to the IA seminar in Anchorage many years ago, the did a speal on seat belts. There is a difference in auto vs. airplane belts, auto are designed to reduce the injury whereas an airplane is supposed to contain the body.
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