I am trying to install a gas dryer. I noticed that the gas pipe from the dryer (yellow) wouldn't lock with the gas pipe coming from the ground. They are both the same size, and I can turn for one thread, but then it becomes impossible. My suspicion is they might have different size thread. I counted 6 threads in approx 11 mm on the pipe coming from the ground and 5 threads in about 8 mm in the flange on the pipe coming from the dryer. My measurements were crude but these come close to a 14 threads per inch on the pipe coming from the ground and 18 threads per inch in the pipe from the dryer.

What would be some of the ways to connect these two? I can't figure out any adapter from Home Depot or Lowe's website.

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  • 1
    A) make sure you thoroughly clean the threads of the pipe coming out of the ground or you won't get a leak proof connection. B) Make sure you thoroughly test all connections, C) Try a local plumbing supply store, not a big box. D) Seriously consider hiring an HVAC guy or plumber to do the hook up to ensure you don't blow up the neighborhood.
    – FreeMan
    Oct 21, 2023 at 21:04
  • A thread pitch gauge is the appropriate tool. Threaded pipe threads are tapered so that they become tighter as you tighten the connection. It may feel like mismatched threads even though it is tightening and sealing as designed. (Ref. NPT Standard Sizes.)
    – HABO
    Oct 21, 2023 at 21:08
  • Thanks for the good point @HABO although I am very puzzled to buy a $8-9 piece. for that purpose. It will most likely sit useless for the years to come.
    – paki eng
    Oct 21, 2023 at 21:14
  • If have have 3/8" x 14 and 3/8" x 18 bolts at hand you can use them to verify that the threads on each side of the connection match the same bolt.
    – HABO
    Oct 21, 2023 at 21:21
  • Don't have those bolts. But thanks for your response @HABO
    – paki eng
    Oct 21, 2023 at 21:23

2 Answers 2


Aside of that very rusty pipe might need replacement using two wrenches (one to hold the vale one to unscrew and replace the pipe)

You need an adapter that looks like this.


Source: adapter

  • Thanks very much.
    – paki eng
    Oct 21, 2023 at 23:13

This 1/2" flare to 1/2" inch FIP coupler did the job. The dryer is happier than ever.

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