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  1. #1
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    Default Metric wonderment experience

    I've been repairing my 35TLB Backhoe and purchased a Tap and Die set that imcluded fine and coarse metric thread components. After I chased a few bolts and threaded metal parts I wondered if my T & D set was out of spec. When I went to purchase new bolts I found out there is also an EXTRA FINE category not included or mentioned in my metric set. At my age (64 today) it is hard to see the difference between fine and extra fine. I was not aware of the extra fine thread category and just wanted to alert all our members. If there are any other unusual metric quirks I may experience and you want to share the knowledge I would appreciate the education.

  2. #2
    Elite Member DieselPower's Avatar
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    Default Re: Metric wonderment experience

    It's not only Metric that has more than two sizes. There are four in SAE. Coarse, Fine, Extra Fine and National Special. I also on rare occasions when working on industrial type manufacturing machinery (usually import equipment) run across a whole other type thread, British Whitworth and oh let's not forget Acme thread.

    Here's a example of how screwed up the US thread system is. Let's use a 3/8 as the example of all the available thread pitch's.

    3/8 - 16 Coarse
    3/8 - 24 Fine
    3/8 - 32 Extra Fine
    3/8 - 18, 20, 27, 28, 40, 48 National Special
    3/8 - 12 Acme
    Last edited by DieselPower; 06-30-2007 at 07:29 AM.

  3. #3
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    Default Re: Metric wonderment experience

    Quote Originally Posted by Edstir
    I've been repairing my 35TLB Backhoe and purchased a Tap and Die set that imcluded fine and coarse metric thread components. After I chased a few bolts and threaded metal parts I wondered if my T & D set was out of spec. When I went to purchase new bolts I found out there is also an EXTRA FINE category not included or mentioned in my metric set. At my age (64 today) it is hard to see the difference between fine and extra fine. I was not aware of the extra fine thread category and just wanted to alert all our members. If there are any other unusual metric quirks I may experience and you want to share the knowledge I would appreciate the education.
    Edstir, I have both inch and metric threads between the accessories and tractor. I understand your frustration with matching thread pitch. What I do is lay the tap and bolt or stud next to each other. When you try to mesh the threads together any difference in pitch will stand out in a fairly short # of threads. If you have a mixture be real careful with diameter too - very close pitch crossovers occur between the 2 systems. Measure your bolt with a caliper. The tap will always be a little bigger than a bolt thread - about 1 or 2%.
    larry

  4. #4
    Super Member _RaT_'s Avatar
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    Default Re: Metric wonderment experience

    Quote Originally Posted by DieselPower
    It's not only Metric that has more than two sizes. There are four in SAE. Coarse, Fine, Extra Fine and National Special. I also on rare occasions when working on industrial type manufacturing machinery (usually import equipment) run across a whole other type thread, British Whitworth and oh let's not forget Acme thread.

    Here's a example of how screwed up the US thread system is. Let's use a 3/8 as the example of all the available thread pitch's.

    3/8 - 16 Coarse
    3/8 - 24 Fine
    3/8 - 32 Extra Fine
    3/8 - 18, 20, 27, 28, 40, 48 National Special
    3/8 - 12 Acme
    Wow, I never knew that. I deal with 1/4-20 and 1/4-28 and stuff like 10-32 but did not realize the others you mentioned existed. Thanks.


  5. #5
    Veteran Member DiezNutz's Avatar
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    Default Re: Metric wonderment experience

    Quote Originally Posted by _RaT_
    Wow, I never knew that. I deal with 1/4-20 and 1/4-28 and stuff like 10-32 but did not realize the others you mentioned existed. Thanks.
    For example if you seen a gear or hub puller, that's Acme
    Kubota B3030-HSD w/R4s, LA403 60" FEL w/ATI TB, RCK60" MMM, Woods BH80-X 4pt Hoe w/24"+12" bkts & Thumb, Woods RB72" Blade w/shoes

  6. #6
    Veteran Member DiezNutz's Avatar
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    Default Re: Metric wonderment experience

    <dang Tab key!>
    But like you, I'm not sure what "National Special" is either?
    Kubota B3030-HSD w/R4s, LA403 60" FEL w/ATI TB, RCK60" MMM, Woods BH80-X 4pt Hoe w/24"+12" bkts & Thumb, Woods RB72" Blade w/shoes

  7. #7
    Super Member mjncad's Avatar
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    Default Re: Metric wonderment experience

    Quote Originally Posted by DieselPower
    It's not only Metric that has more than two sizes. There are four in SAE. Coarse, Fine, Extra Fine and National Special. I also on rare occasions when working on industrial type manufacturing machinery (usually import equipment) run across a whole other type thread, British Whitworth and oh let's not forget Acme thread.

    Here's a example of how screwed up the US thread system is. Let's use a 3/8 as the example of all the available thread pitch's.

    3/8 - 16 Coarse
    3/8 - 24 Fine
    3/8 - 32 Extra Fine
    3/8 - 18, 20, 27, 28, 40, 48 National Special
    3/8 - 12 Acme
    Of course, let's not forget NPT (National Pipe Thread) that are the tapered pipe threads. According to my 21st edition of Machinery's Handbook, we have the following pipe threads:

    NPT - American National Standard Taper Pipe Thread
    NPTR - American National Standard Taper Pipe Thread for Railing Joints
    NPSC - American National Standard Straight Pipe Thread for Couplings
    NPSM - American National Standard Straight Pipe Thread for Free-fitting Mechanical Joints
    NPSL - American National Standard Straight Pipe Thread for Loose-fitting Mechanical Joints with Lock-nuts
    NPSH - American National Standard Straight Pipe Thread for Hose Couplings

    Then there is:

    NPTF - American National Standard Dryseal Taper Pipe Thread for Pressure-tight Joints

    ...and the variations of:

    NPTF-SAE Short - Dryseal SAE Short Taper Pipe Thread
    NPSF - Dryseal ANSI Standard Fuel Internal Straight Pipe Thread
    NPSI - Dryseal ANSI Standard Intermediate Internal Straight Pipe Thread

    Let's not forget square threads, which are similar to ACME; but aren't.

    To paraphrase Mr. Spock from the episode "I Mudd", "There is a coarse thread, a fine thread, an extra fine thread, a taper thread, a dryseal thread, a whole plethora of threads; but only one ACME thread."

    I wonder how many of these thread types are still in existence. Does anyone have the latest (27th I believe) edition of Machinery's Handbook to verify?
    Paraphrasing Douglas Adams - So long and thanks for all the bacon.

  8. #8
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    Default Re: Metric wonderment experience

    Thanks to all that responded. I have been enlightened. The local jobbers I been to for hardware are bewildered when it comes to metric. Menards has a new bolt display with coarse and fine but no extra fine that I could find. I think I will order bolts by their specific kubota part number to make sure I have the right kind. Metric tools are easy to find but the hardware leaves a lot to be desired.

  9. #9
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    Default Re: Metric wonderment experience

    Extra fine is not very common.

    Usually you only use metric coarse, I dont think I have ever used anything else.

  10. #10
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    Default Re: Metric wonderment experience

    Quote Originally Posted by Mith
    Extra fine is not very common.

    Usually you only use metric coarse, I dont think I have ever used anything else.
    Kubotas use fines.
    larry

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