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Schrader Valve thread

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  • Schrader Valve thread

    Had a job in to day that required a Schrader valve thread tapping into an alloy block for a small machine.

    Now I know these are special so looked it up and found the following at various places.

    According to the Tire and Rim Association (and they should know) the standard Schrader valve has the following thread

    7.7 mm OD

    32 tpi, or 0.794 mm pitch

    Minor diameter is 6.9mm

    Thread designation is .305-32 or 7.7-32

    So not having the correct tap and before I decided to make one I though I'd see what was close.
    There is a 5/16" x 32 [ 0.3125 x 32 ] listed as Model Engineer thread so drilled a scrap piece of alloy and tapped this and tried the sample supplied to see how loose it was .
    Went in about 3 or 4 threads by hand and stopped ?

    Measured the supplied valve and it was 0.302" x 30 ??? not 32.

    Hunted round in the "Get John out the sh1t drawer ] and came up with two 5/16" x 30 taps, [ no spec on them ]

    Tapped the scrap piece of alloy and bingo slightly loose but nothing a dab of loctite won't handle.

    Next question, has anyone else come across this before ?

    I don't have any more valves to check , this was the type that's threaded all the way down to the tube, not the moulded type.

    .
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.




  • #2
    I couldn't find a tap either so when I needed to thread one I just used a simple thread restorer...Don't know if it will work for your application. The one's I had were all 32 tpi.



    http://www.brandsplace.com/0246-mils445.html
    Last edited by Mike Burdick; 01-13-2009, 10:34 PM.

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    • #3
      Yes,several odd threads I have found,the .305-32 you mention,a 5/16-28 and a 1/16 straight pipe thread and those are just the small stems.
      I just need one more tool,just one!

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      • #4
        i just looked into the schraeder threads like two weeks ago and it struck me as odd that such an oddball thread would be used on such a popular item...
        -paul

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        • #5
          Just went out to the garage and pulled out several to measure and they were all .301 - .304 and 32 tpi.

          Aren't standards wonderful - there are so many we can deviate from.

          Glenn

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          • #6
            Mcmaster -carr sell schrader valves in standard and non-standard threads, I bought standard thread valves when I was making some air fork cap nuts for a motocrosser.
            Non, je ne regrette rien.

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            • #7
              I screwcut a schrader male adapter one day I had forgot my glasses,couldn`t even see the thread but it held 2000 psi of nitrogen to get an accumulator charged.Threw it away as soon as possible in case some one seen it.

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