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Thread: Excess threads?

  1. #1

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    Excess threads?

    Starting this thread so I don't hijack Buzzcola's. In his inspection, the Fed made him add a washer to keep less than 3 threads showing.

    Could someone please enlighten me? What is the problem here from an engineering standpoint?

    Thanks, John

  2. #2
    Steve Pierce's Avatar
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    As long as the nut is not bottomed out on the bolt I see no issue and don't recall seeing anything in the 43.13 either.
    Steve Pierce

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  3. #3

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    I think there is something on stacking washers though in 43.13. Maximum combined height of washers is 1/8”

  4. #4
    Buzzcola777's Avatar
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    Basics of Bolt Installation
    Certain accepted practices prevail concerning the installation of hardware. A few of these regarding bolt installation follow:


    • In determining proper bolt length - no more than one thread should be hidden inside the bolt hole.
    • Whenever possible, bolts should be installed pointing aft and to the center of an airplane.
    • Use a torque wrench whenever possible and determine torque values based on the size of bolt.
    • Be sure bolt and nut threads are clean and dry.
    • Use smooth, even pulls when tightening.
    • Tighten the nut first - whenever possible.
    • A typical installation includes a bolt, one washer and a nut.
    • If the bolt is too long, a maximum of three washers may be used.
    • If more than three threads are protruding from the nut, the bolt may be too long and could be bottoming out on the shank.
    • Use undrilled bolts with fiber lock nuts. If you use a drilled bolt and fiber nut combination, be sure no burrs exist on the drilled hole that will cut the fiber.
    • If the bolt does not fit snugly consider the use of a close tolerance bolt.
    • Don't make a practice of cutting off a bolt that is too long to fit a hole. That can often weaken the bolt and allow corrosion in the area that is cut.
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  5. #5
    aeroaddict's Avatar
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    Interesting as I have never heard there is a MAXIMUM on threads protruding.
    Worked in aerospace for my career (not as a mechanic) and there was a rule that there had to be a minimum of 1 1/2 threads showing past the top of the nut. As Steve mentioned, as long as the nut hasn't bottomed out, I would think it doesn't matter how many threads are sticking out.

    Not to say that proper bolt length should always be used.

  6. #6
    supercrow's Avatar
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    And you can feel a nut bottoming out instantly.

  7. #7
    irishfield's Avatar
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    On a typical AN3 bolt, using an AN365-1032 nut... if you get to 4 threads showing you have bottomed the nut on the shank. Why the "no more than 3 threads showing" regulation.

    For any that have built a Murphy wing, with the numerous AN3 bolts in the spar backer strip, if you don't add an additional washer the nut bottoms on the bolt shoulder JUST before it has actually squashed the backer to the spar. You can't tell the difference as to whether you actually bottomed it or pulled the parts together.
    Last edited by irishfield; 06-06-2021 at 07:09 PM.

  8. #8

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    Thanks guys. So the 3 thread rule is a good rule of thumb for a quick inspection, but the real rule is "don't bottom out the nut on the threads". Got it.
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  9. #9
    wireweinie's Avatar
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    To many different types of nuts to go by number of threads showing. Use the parts manual or measure. This clip is from the AC43.13-1B.

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  10. #10

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    Not only different nut types, but the bolt combinations are many as well. If you’re looking for tightening up tolerances in looser holes, higher grip/tensile strength than AN hardware can provide, etc, don’t overlook the NAS and MS series bolts, screws, etc. Do your research and pay attention to grips and thread lengths. They are NOT the same as AN in dash number, the threads can be longer or shorter (usually shorter) but can provide you with options you wouldn’t otherwise have for increased strength, serviceability, and hardware accuracy issues.
    I highly recommend a shop copy of the GENUINE AIRCRAFT HARDWARE book.
    A cruise through their website is always good too. Great reference and maintenance resource.


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  11. #11

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    [/ATTACH]Click image for larger version. 

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  12. #12

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    They call it their “Big binder reference book”


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  13. #13
    cubdriver2's Avatar
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    Mike had an app for just this

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  14. #14

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    Mikes app only covers the formula for AN bolts. It’s a great help but won’t work with NAS and MS hardware because of differences in how the dash numbers for length and in some cases length, part numbers, etc are calculated.
    Obviously Piper didn’t use or even need to use this different “specialty” hardware but if a person gets familiar with some of this stuff it can save time, quite often some parts that would otherwise be too worn to use, better grip length options, etc.
    NAS bolts for example can be had in 1st and second oversizes, far beyond even the close tolerance sizing. Gives a person options. “X” bolts are .0156 over and “Y” bolts are .0312 oversize without an increase in thread size so the size of the nuts used remain the same. Just a couple tidbits, maybe useful for some folks here and elsewhere.

    Cheers, Oz


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  15. #15
    RVBottomly's Avatar
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    Quote Originally Posted by OzAK View Post
    I highly recommend a shop copy of the GENUINE AIRCRAFT HARDWARE book.
    A cruise through their website is always good too. Great reference and maintenance resource.


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    Thanks for that. I hadn't run across them before. Now I have an account and a reference book coming. Looks like I should have known about this 3 years ago.

  16. #16

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    RV, that’s great! It’s gratifying to know that even if it’s just one person, passing on some info helps make someone’s life and experience easier. Enjoy the info. It’s an amazing collection.


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