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  • plumbing rules of the (dirty) thumb

    just curious to know if anybody has ever been taught, or figured out really good rules of thumb that work for you.

    i do realize that there are seasoned plumbers and pipefitters that could teach me many things about threaded joints. this is more for the young men just starting in the trades.

    the one that i use most has to do with pipe threads and fittings. i've mentioned it before and i do think it's worth mentioning again. it has saved me from the frustrating fittings/nipples/pipe joints that used to leak when i installed them. of course that's when i was a younger man.

    Northern Alberta Institute of Technology rule of thumb;

    3 threads should be visible after tightening. anymore or anyless should make you question the joint.

    either the fitting/nipple/pipe thread is bad, or it's crossthreaded.

    too little thread (bottoming out) showing is either;

    -male thread is cut too deep
    -female threads where cut too deep from the factory
    -the fitting is used and stretched.

    too much thread could be one of the following;

    -male thread not cut deep enough
    -female thread on fitting not cut deep enough from the factory
    -crossthreaded

    save yourself the headache and embarassment of the joint leaking in front of the customer, not to mention the call-back.

    works for me everytime.

    ps if i missed something please tell me.

  • #2
    Re: plumbing rules of the (dirty) thumb

    I like to go one step farther with this one. I use the 3,3,3 rule of thumb. It should thread by hand 3 full turns then 3 with the wrench and last but not least 3 threads showing

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    • #3
      Re: plumbing rules of the (dirty) thumb

      Those are good rules to use

      I have noticed that past few years that the quality of the fitting has dropped off. We now use mostly imported fittings from Taiwan. It seems that I can tighten these up almost all the way to where there are no more threads showing without great force being applied. I know my dies set and are working perfectly.

      I only buy the imports when doing hydronics. Still pay the premium for gas fittings because it only takes one leak to wipe out any savings in the cost.

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      • #4
        Re: plumbing rules of the (dirty) thumb

        No. 1 rule, check your face before you get out of the van.

        I went into the local grocery store to buy a sandwich and the cashier just kept smiling at me and I loved it. I strutted out to my van knowing I "still had it". I was eating my sandwich when I looked in the mirror and saw a large white streak on my forehead of Great White pipe dope. JOY KILL.


        You can be the best plumber in world with loads of knowledge but if your appearance is poor and your tools in terrible shape it will greatly affect what coworkers and customers think of you, justified or not.
        Anyone can tear a man down, few can build one up.

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        • #5
          Re: plumbing rules of the (dirty) thumb

          I snug up to a point where it won't easily turn, and I've never paid attention to # of threads given that some connections are loose, some are tight.

          The black iron fittings I use come for two/three different areas of the world and it sucks when one will bottom out on the threads.
          Northern Kentucky Plumbers Twitter Feed | Plumbing Videos

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          • #6
            Re: plumbing rules of the (dirty) thumb

            If you look at the ANSI spec for pipe threads, it gives a chart by pipe size, as to how many hand tight turns, how many wrench turns, how many threads on the pipe and fittings. BUT, it actually has a note that since field cut threads often do not conform completely to the spec, then the experience of the pipefitter needs to come into play as to how to determine proper assembly.

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