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Thread: Min Internal Thread Engagement Length

  1. #1
    Associate Engineer
    Join Date
    May 2013
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    Min Internal Thread Engagement Length

    Hello everyones.

    I'm new in this forum.

    I have a question on screw tapping hole.

    If drawing only specify M2.5, what is the thread length here? Do we have a standard calculation here?

    With Unified screw, it's engagement length is specified in a standard no. of thread per inch.

    Then I wonder what is the standard for metrice thread?


    Thank you very much!!

  2. #2
    Technical Fellow jboggs's Avatar
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    Mar 2011
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    Please check your words. You ask for thread length, which means the distance from the first thread to the last thread. Then you mention "thread per inch". That is thread pitch, the distance from one thread to the next. Which do you want: thread length or thread pitch?

    In my experience with metric threads, if no pitch is specified, assume standard coarse pitch.

  3. #3
    Associate Engineer
    Join Date
    May 2013
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    Quote Originally Posted by jboggs View Post
    Please check your words. You ask for thread length, which means the distance from the first thread to the last thread. Then you mention "thread per inch". That is thread pitch, the distance from one thread to the next. Which do you want: thread length or thread pitch?

    Thanks for your reply, jboggs.

    In my experience with metric threads, if no pitch is specified, assume standard coarse pitch.
    I'm asking for the standard of thread length (min engagement length).

    I'm sorry to create the confusion.

  4. #4
    Technical Fellow
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    Feb 2011
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    I'm with JB, it is very unclear what you are after, but, if it is thread engagement the a rule of thumb is a minimum of one diameter.

    However it seems more likely that you are after Pitch in which case, if omitted in ISO it is the Pitch for a standard course thread, in your case, M2.5 x 0.45

    BUT - it is always best to check back with the customer as they will be the one rejecting 20,000 items you have just machined with the incorrect pitch.

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