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Tap size for NPT threads, Now drill bits to.

Discussion in 'The Garage' started by rugger03, Jun 30, 2003.

  1. rugger03

    rugger03 1/2 ton status

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    Need to tap a few holes in my ehaust and intake manifold, but a little confused about the proper size taps i need. The pyrometer needs a 1/4" npt threaded hole, and the boost gauge needs a 1/8" npt what size taps are these my tap set only has fine and course thread taps, im guessing NPT are the course thread but want to make sure. So i guess what im looking for are the how man thread ber inch i need for these two fittings. any help is appreciated.
    cheers, rugger
     
  2. heavy4x4

    heavy4x4 1/2 ton status

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    Re: Tap size for NPT threads.

    You need NPT (pipe thread) taps. You can't use standard fine or course thread taps - they aren't the same at all.

    You can find them at your local ACE hardware.
     
  3. rugger03

    rugger03 1/2 ton status

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    Re: Tap size for NPT threads.

    Cool, thats what i thought. Just wanted to make sure before i left the house.
    thanks, rugger
     
  4. Stomper

    Stomper ΜΟΛΩΝ ΛΑΒΕ GMOTM Winner

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    Re: Tap size for NPT threads.

    And when you tap with npt taps, it's not the same as with "un" taps. There is a specific depth that the npt tap needs to go to. So if you tap to deep, to shallow or all the way through, your threads won't seal. Just take you time /forums/images/graemlins/thumb.gif
     
  5. DieselDan

    DieselDan 1/2 ton status

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    Re: Tap size for NPT threads.

    Just to add to what stomper said... Look at the NPT tap or NPT fitting. You can actually see the taper from the begining to the end of the threaded area. Machine threads (like bolts) don't have this taper. When cutting NPT threads for sensors and such start at the begining of the tap then stop BEFORE you get carried away. Check the depth of sensor by screwing that in your new hole /forums/images/graemlins/blush.gif If the sensor needs to sit deeper in, unscrew it and and give the tap a few more twists. Throw some teflon tape or paste on the threads and call it good. Also DON'T over torque a NPT fitting (or sensor). I've seen manifolds, goosenecks, oil coolers, etc. crack from some overzealous cranking /forums/images/graemlins/mad.gif
     
  6. Don

    Don 1/2 ton status

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    Re: Tap size for NPT threads.

    When You go to buy pipe tap's, read the side, or look at a chart, they take an oddball sized drill bit for the hole too. /forums/images/graemlins/eek.gif
     
  7. rugger03

    rugger03 1/2 ton status

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    Re: Tap size for NPT threads.

    Hey all thanks for the help, i made my purchase of 2 hason taps tonight. I plan on doing the initial tap just until it is visible out the other side then if it needs to be opened up more i can do so later. \

    For all you in the know can you recomend a good set of drill bits, not a cheap set but some good life time investment ones? Can't get answer from anyone at a store; cobalt, Zirconium, titanium etc. I just want a good set that can handle drilling in steal and ocasional wood if such a thing exsits. I might wrongly assume if it can drill metal wood won't be a problem.
    Thanks again,
    rugger
     

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