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Thread: Specification for NPT Taps

  1. #1

    Specification for NPT Taps

    Is there a standard that governs the tap used to cut NPT threads? I am particularly interested in 1/4-18 NPT. I am creating a fixture to support a tap. It will need to surround the shaft of the tap and I need to know if a standard governs the size and tolerance of the shaft.

    Below is a picture of what I am trying to get a specification on. It is the body of the tapping tool.
    Attached Images Attached Images
    Last edited by hogpaw; 05-20-2013 at 11:31 AM.

  2. #2
    Administrator Kelly Bramble's Avatar
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    NPT = National Pipe Thread, ANSI/ASME standard B1.20.1.

  3. #3
    I uploaded a picture on the initial post that shows what part of the tapping tool I am trying to find a dimension and tolerance for.

  4. #4
    Technical Fellow jboggs's Avatar
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    When you asked the manufacturer what did he say? What? You didn't ask the manufacturer? Hmm...

  5. #5
    jboggs,

    There is more than on manufacturer of NPT taps, hence my initial question: Is there a standard that governs the manufacture of NPT taps?

  6. #6
    Technical Fellow jboggs's Avatar
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    "Is there a standard that governs the manufacture of NPT taps?"

    Who would know the answer to that question better than a manufacturer?

  7. #7
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    Hogpaw, listen to JB! At a guess I would say there probably is a loose standard that is more of convenience than ideal. I suspect the shank diameter will be dictated largely by the square on the top. The square, which does have a specification for will probably define a convenient diameter shank.

    Lemme just say more Bytes and say again, listen to JB.

  8. #8
    Lead Engineer RWOLFEJR's Avatar
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    Per ANSI B94.9-1979
    1/4-18 NPT Shank Diameter is .5625 +.000 / -.002 if ground threads. Shank Dia. is .5625 +.000 / -.007 if cut threads.
    Square drive on the tap will be .421 +.000 / -.006

  9. #9
    Awesome suggestion JBoggs!!! Got the info I needed....from the Mfr.

  10. #10
    Thank you rwolfejr

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