Metric Thread Headache


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    Default Metric Thread Headache

    From as much research as I was able to do, metric taps use pitch which is the reciprocal of TPI (threads per-inch)

    So a M10x1.0 tap has 1 tooth per 1MM which is 1 tooth per .03937inch. 1/(.03927) means there's 25.4 teeth per 1inch.
    I just want to make sure that I am understanding metric taps properly before I put my theory to test on the machine.
    Although I'm pretty confident in my research, I'm completely confused when I test that research with physical gauges we have at the shop.
    When I put the teeth of a 6-32 up to the teeth of a 10-32 the two conform and prove to me that they have the same pitch.
    When I put the teeth of a M10x1.0 up to a M5x1.0 they do not conform... That has me soo confused.
    When I measure/count the teeth of a M10x1.0 it seems that there is about 16 teeth per inch.

    Please help.

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    Default Re: Metric Thread Headache

    Are you sure your M10 tap has 1mm pitch? Normal (coarse) M10 has 1.5mm pitch (about 17tpi ) and normal M5 has 0.8mm pitch (about 32tpi). M10x1 is possible - but considered "fine pitch". M5x1 will be some sort "special - extra coarse" (or "we did'it to make sure you cannot buy third party spares" )
    See Threads - Metric ISO 724 for reference



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    Default Re: Metric Thread Headache

    You raise a good question. The gauge itself just says M10. It isn't labeled M10x1.0. I will look into that.



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    Default Re: Metric Thread Headache

    +1 on grg12 reply. You're rigth on your understanding and theory about metric threads; but unless they're custom made, I don't believe you can ever find an M10 matching a M5 bolt.



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    Default Re: Metric Thread Headache

    Here is a metric thread chart showing all the variations.

    Attached Thumbnails Attached Thumbnails Metric Thread Headache-metricthread-jpg  
    An open mind is a virtue...so long as all the common sense has not leaked out.


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    Default Re: Metric Thread Headache

    You were right on. The M10 tap turned out to be M10x1.5 and the M5 turned out to be M5x0.8 That really makes me wonder why the pitch isn't labeled on the gauge. Is it because those tap diameter are standard with that tap pitch? It was interesting to tell the inspectors that their gauges were miss placed and need better labeling. I put the M10 up to a M14x1.5 gauge and they conformed. The M5 conformed with its bigger counter-part M5x0.8 STI. The world of threads makes sense again. All is well. Ty guys.



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    Default Re: Metric Thread Headache

    And Geof,

    Thanks for the comprehensive chart. Quite useful.
    Here it is as a PDF,

    Neil

    Attached Thumbnails Attached Thumbnails Metric Thread Headache-metricthreads-pdf  
    Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. THREE ways to fix things: The RIGHT way, the OTHER way, and maybe YOUR way, which is possibly a FASTER WRONG WAY!


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    Default Re: Metric Thread Headache

    If the gage says M10 than that is always standard coarse. It is the coarsest thread available for M10. If you see a thread M10 x 1 than that is metric fine. The whole world designates metric (coarse) by not given a pitch. If you see a pitch listed with a nominal thread size than that is a "FINE" thread.
    All this worked fine until US manufacturing started working in metric and ANSI screwed it up by allowing the pitch to be listed on coarse thread because Americans are so used to having a pitch (Number of threads per inch) listed. Now when you see a US metric print with the pitch listed next to the nominal size you need to look in a book to understand what kind of thread you have and what tap you need. Prints from the rest of the world do not list a pitch unless it is a "Fine" thread.
    95% of all metric threads are coarse. Most shops do not stock any kind of fine screws or fine taps and dies. It is only when you get into special purpose threads that you find threads with a fine pitch.
    ANSI most likely felt they did US a favor by listing the pitch on standard coarse. After all what harm could it do? It is only when you start working with metric prints that you realize just how bad they screwed up.
    I can not count the number of times we have received inquiries on prints - what is the pitch????? When you tell them M10 x 1.5 than they will start looking for a tap marked M10 x 1.5. Not realizing that this is the standard tap M10 available in every store.
    You go and order a M10 screw or an M8 nut and nowhere in the world will anybody ask M10 by what? Or M8 by what. The idea is to save money by reducing inventory on screw sizes, nuts, taps and dies.
    I hope this helps a little bit.



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    Default Re: Metric Thread Headache

    Just a note from this ole American guy.
    This is the FIRST time I have ever seen the fact that a Mx means that it is the course thread.

    Thank YOU!

    Art
    AKA Country Bubba (Older Than Dirt)


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    Default Re: Metric Thread Headache

    And to add to the simplicity, if you drill a 10mm hole, there is some clearance to the thread due to rounded top on thread.
    It will measure something like 9.85mm
    Tapping drill size is diameter minus pitch. That's it. too easy?
    And I can handle inches just as well. I drill 5.1 for a 1/4-20

    Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. THREE ways to fix things: The RIGHT way, the OTHER way, and maybe YOUR way, which is possibly a FASTER WRONG WAY!


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    Default Re: Metric Thread Headache

    the 10x1 is a fine thread
    5x1 not exist, but 5x0.8 the normal or coarse thread..

    world is metric, but usa :-)

    even the most conservative nation, england using metric..


    for metric is defined the thread """length""

    for inches defined the count per inch..

    that what confusing you..
    im coming from metric, and took quite a time getting familiar with 1/8 and its alternative the 0.125...
    for construction industry the franction quite good.. nothing need to be more precise than 1/8 on a house..

    for machineshop the metric works better.. 0.1 mm for manual works with file, and for machine work 0.005 mm already a ground surface..so using less digits makes simpler to memorizing tolerances...

    additionally, i dont see the least chance that it will change ever :-)



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    Default Re: Metric Thread Headache

    under 10 mm the normal thread, as a thumbrule you can use drill multiplying the M# with 0.8...

    for example M8 thread you need 6.4 drill bit.. using larger by 0.1 mm makes easier the tapping..



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    Default Re: Metric Thread Headache

    Multiply M# by 0.85 is much closer, else you will be really pushing it in steel, still easier to subtract the pitch! (in your head)
    Then it is correct. All taps have the pitch written on them, so nothing to look up.

    Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. THREE ways to fix things: The RIGHT way, the OTHER way, and maybe YOUR way, which is possibly a FASTER WRONG WAY!


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    Default Re: Metric Thread Headache

    Metric standard pitches can be made in any size.

    Thus a standard 0.5 mm pitch, can be put on any size bolt. The sizes refer to fractions of the pitch.

    I have 10 MM x 0.5 mm pitch, taps and dies. Standard on fine laboratory adjustment screw, similar to micrometers.

    All this is explained in the machinerys handbook, and online in wikipedia referring to threads and pitches.

    Metric is exact and precise . Thus use of "fine" and "coarse" is discouraged - instead you refer to the exact pitch.
    Thus M10 is standard, M10x1.5 is fully defined, and M10x0.5 is fully defined.

    M10x0.5 is not *common* - but is a correctly specified thread.
    The accuracy and tolerance is specified separately.

    Thus a M3x0.5 standard thread is exactly the same size as a M10x0.5 standard thread, but the M10 is on a bigger bolt (and stronger, more rigid).

    Great explanation here:
    ISO metric screw thread - Wikipedia, the free encyclopedia



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