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  1. #1
    MasterAlex's Avatar
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    4-40 Bolt - What's this mean?1

    Okay, in the "there's no such thing as a stupid question" category - he's my last one for the year

    The last time I flew my SSE the canopy bolt jettisoned itself from the airframe during a series of aileron rolls. Silly me it was the 3rd or 4th flight of the day on that plane and the bolt must have worked itself loose [:@] - I should've checked it, I know. Fortunately, the canopy stayed on the plane!

    Anyway, I have been trying to find a replacement for this little bugger and I am at a loss; well, probably not, but I need some guidance from you guys. The bolt is 4-40 1" nylon. Now here's the aforementioned question:

    What does 4-40 mean? 4mm by ?? ... is the second number the number of turns on the thread every inch? What's the secret code here? I have been to several hardware stores and have not seen any hardware with the 4-40 nomenclature. Is this also known under some other branding?

    Can someone please unlock the mystery for me??

    Thanks!!
    \"What you do off the job is determining factor in how far you will go on the job\" - how appropriate for us RCers!

  2. #2

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    RE: 4-40 Bolt - What's this mean?1

    You have a size 4 bolt with 40 threads per inch. 4-40X1/2" Now you have the length. Here is a bolt chart:

    http://store.nutsandbolts.com/threads-per-inch.html

    http://www.ligo.caltech.edu/docs/T/T030118-01.pdf

    ORIGINAL: MasterAlex

    Okay, in the "there's no such thing as a stupid question" category - he's my last one for the year

    The last time I flew my SSE the canopy bolt jettisoned itself from the airframe during a series of aileron rolls. Silly me it was the 3rd or 4th flight of the day on that plane and the bolt must have worked itself loose [:@] - I should've checked it, I know. Fortunately, the canopy stayed on the plane!

    Anyway, I have been trying to find a replacement for this little bugger and I am at a loss; well, probably not, but I need some guidance from you guys. The bolt is 4-40 1" nylon. Now here's the aforementioned question:

    What does 4-40 mean? 4mm by ?? ... is the second number the number of turns on the thread every inch? What's the secret code here? I have been to several hardware stores and have not seen any hardware with the 4-40 nomenclature. Is this also known under some other branding?

    Can someone please unlock the mystery for me??

    Thanks!!

  3. #3

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    RE: 4-40 Bolt - What's this mean?1

    The 4 is a number that relates to the size--I don't think it is directly related to any standard unit of measure. Commonly used sizes in modeling are #2, #4, and #6. A #12 is essentially a 3/16" diameter. Bigger than that you will see decimal sizes. And yes, the 40 refers to number of threads per inch. MOst big box stores don't carry anything smaller than #6.

  4. #4

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    RE: 4-40 Bolt - What's this mean?1

    q

  5. #5
    Hill202's Avatar
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    RE: 4-40 Bolt - What's this mean?1

    ORIGINAL: MasterAlex

    Okay, in the "there's no such thing as a stupid question" category - he's my last one for the year
    For me, your question falls into the "you learn something new every day" category. I also did not know what 4-40 means .

    Now I do.
    Grammar: The difference in knowing your sh*t and knowing you\'\'re sh*t.

  6. #6
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    RE: 4-40 Bolt - What's this mean?1

    Low-Depo won't have anything that small. You'll have to mail order it. Try RTL Fasteners (http://rtlfasteners.com.) You can order a bunch of small hardware for a good price and not pull your hair out trying to find the right fastener when you need it.
    It was a gravitational altitude correction. AMA 82823

  7. #7

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    RE: 4-40 Bolt - What's this mean?1

    As stated. the No. 4 refers to the diameter of the screw. In the case of the 4-40, it is .112 inch.
    If all else fails, send me your mail address and I will mail you a couple of 4-40 x 1".
    Direct: eloym@dslextreme.com

  8. #8
    firstplaceaviator's Avatar
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    RE: 4-40 Bolt - What's this mean?1

    Ace Hardware might have them. Our local Ace has a huge selection of tiny hardware[8D]

  9. #9
    Jim_Purcha's Avatar
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    RE: 4-40 Bolt - What's this mean?1

    Check with fastenal or other industrial fastener suppliers.

    Jim
    Ultra Sport Brotherhood #30

  10. #10
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    RE: 4-40 Bolt - What's this mean?1

    Thanks to everyone that's responded!! I feel better knowing this. I was in my local ACE this morning and they do carry micro hardware (I bought a 2.6 mm x 12 mm screw) - now that I know what 4-40 means, I'll check their stock so see if they've got it. Otherwise, I'll probably go the RTL as I need to place an order with them anyway.
    \"What you do off the job is determining factor in how far you will go on the job\" - how appropriate for us RCers!

  11. #11
    MasterAlex's Avatar
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    RE: 4-40 Bolt - What's this mean?1


    ORIGINAL: fancman

    You have a size 4 bolt with 40 threads per inch. 4-40X1/2" Now you have the length. Here is a bolt chart:

    http://store.nutsandbolts.com/threads-per-inch.html

    http://www.ligo.caltech.edu/docs/T/T030118-01.pdf
    Fancman ... awesome links! Thanks.
    \"What you do off the job is determining factor in how far you will go on the job\" - how appropriate for us RCers!

  12. #12
    Hawkeye's Avatar
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    RE: 4-40 Bolt - What's this mean?1

    Master Alex,
    If your Ace store doesn't have it, any LHS will have it in the Dubro section.
    Also, one of the questions you asked was "What's the secret code here?". Here's the secret code so you can figure any number size thread.
    First of all, numbered thread sizes are below 1/4" dia and go up to about #14, although I've never used any above #10.
    The code is : ( and don't tell anyone, because it's a trade secret!!) As you know the second number is the number of threads per inch. The mysterious first number is the outside diamater fo the thread. To figure the diamater, in thousanths of an inch, you multiply the first number (in your case: 4) times .013" and then add .060" to that number.
    So... 4 X .013" = .052". Add to that .060" and you get .112" dia as EloyM mentioned. This works for all the number size threads.
    ...Steve


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