We have installed a new gas cooktop. I am connecting the 1/2” gas line. I have the flexible line connected to the cooktop pressure regulator.

Coming from the wall, we have 3/4” threaded black pipe, connected to an elbow ball valve. I am unfamiliar with the large male (flare?) fitting at the end of the valve. valve attached to pipe

Looking at the hardware store this seems to be 15/16” flare male. However, I can find nothing that would connect this with my 1/2” flexible gas line installed to the cooktop. If it is helpful, I have measured the exterior diameter of the smooth portion (after the threads) of the male fitting with calipers at just over 13/16”.

UPDATE: Measuring the exterior of the male threads is 15/16".

While I would rather not, I could turn-off the gas and remove the valve. In this case, I am not certain of the best fittings to connect from the 3/4” black pipe, to include an elbow and a ball valve to connect with the 1/2” flexible gas line.

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    Check with your local inspectors since some areas don't allow homeowners to connect gas appliances. Call your gas company and they'll probably do it for free and check the rest of your system.
    – JACK
    Aug 16, 2021 at 22:24
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    If you don't want to shut the gas to replace the valve then you can probably find a flexible gas line to connect to it. Then on the stove end you'll need to get a fitting to connect the flexible gas line to the stove. The flexible line usually comes with extra fittings but you may need to get an additional fitting. Post a picture of the fitting on the stove side and you'll get a better answer. The correct way to measure is the outside of the threaded portion not the smooth portion of the fitting. Aug 17, 2021 at 2:39
  • @PlatinumGoose my reading is that the OP already has a flex line, but cannot get it coupled to the valve. It seems that you're telling him to get a flex line to couple to it. Have I completely misunderstood you?
    – FreeMan
    Aug 17, 2021 at 15:44
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    @FreeMan he has a 1/2 flex line which won't fit the gas valve he has. He doesn't want to change the gas valve so he probably needs a 3/4" or 1" flex line to connect to the gas valve. Then he would need an adaptor on the stove side. I didn't post as an answer because there's plumbing people here that can tell him the easiest and most cost effective way to connect it. Unfortunately when it involves gas people are reluctant to help out over concern for the poster. Aug 17, 2021 at 17:07
  • @PlatinumGoose gotcha! It was my misreading, then.
    – FreeMan
    Aug 17, 2021 at 17:09

1 Answer 1


The Flare Fitting

If you want to measure the flare with calipers, then you need to measure around the outside of the male threads or the diameter of the hole. The angle of the flare appears to be 45 degrees, and assuming that your threads are 1+1/16 inch, then the hole is 3/4 inch. That is an unusual size for flexible pipe which is usually 5/8 or 1/2 inch. I searched for a 3/4" female flare to 5/8" male flare, but had no luck. I am sure someone wants to sell such a thing, but I have no idea who.

National Pipe Thread

The tapered threads on iron pipe do NOT create a seal. Pipe sealant is required. I like to the blue stuff, but that is a personal preference. Apply a small measure to the first few threads. Do not get any inside the pipe or it might end up in your appliance and cause problems.

How Tight

Tighten a gas line until the tightening resistance does not increase. Make sure some threads remain showing or the junction will leak. A 1/2 inch pipe is not difficult to tighten. Bigger pipes require more torque. Smaller pipes requires less torque.


Do NOT do this because I am NOT liable for any B.S. in this liability loving country filled with citizens that are allowed to blame their personal ineptness upon others...

A capable man would turn off the gas outside at the meter and replace the valve. He would also make sure that the pipe in the wall does not turn as he works. He would then remove the uncommon valve and install:

One 3/4 street 90. One 3/4 x 1/2 reducing bell (bushings are against code because they cannot be tightened one thread at a time). A short nipple with enough between to attach a wrench without damaging the threads (fully threaded nipples are against code because they cannot be tightened one thread at a time). Note: Amazon is selling a beautiful stainless 3/4 female x 1/2 male reducer which would perform the conversion in one step. Lastly, a 1/2" gas shut off valve.

Now you have a standard fitting. Turn the gas back on outside and check that the fast moving pointer is not moving. With a marker, carefully position your head and mark the position of the needle that moves quickly when gas is getting used. Wait 30 minutes, more is better. If the fast moving pointer moved, then you have a problem. There are a million rules involving gas, especially when older appliances exist anywhere in the home. Remember what I told you: Do NOT do replace the valve yourself. You might learn something at a large cost.

Off Subject

The more you tinker, the more you tinker, and the more you learn the better: An abandoned line left with just a valve, it needs a cap. I like reasonable codes for reasonable safety. I think codes reached their reasonable peak around 1980. Since then, safety codes have been moving into unreasonable fear backed by unreasonable liability. You may have lost the right to repair your car, your computer, and your phone, but at the current time, you still have the right to repair the house that you live in and own.

  • Agree with last paragraph. Enough videos around of the unexpected rapid deconstruction of houses. People should leave any gas work to professionals(at least insurance will pay then).
    – crip659
    Aug 17, 2021 at 12:49
  • I added the outside thread measurement of the male flare : 15/16". I am certain about the black pipe being 3/4" the outside diameter is 1 1/16". No one who provides any answer or comment has any liability to me. I am comfortable threading and connecting black pipe, I like to use the yellow tape. I test using a leak detector spray. I should check the meter as well, thanks for the reminder. I secure upstream items when tightening/loosening downstream parts.
    – Degan
    Aug 17, 2021 at 21:42
  • It is not you we are worried about, it is your and your neighbours insurance companies. Too many houses have become toothpicks, because of gas boo-boos(sometimes done by professionals). There might be adapters for you to use, or might need to change the hose. A gas installer would have the correct answer, more than us idiots online.
    – crip659
    Aug 17, 2021 at 22:17
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    Professionals doing the same thing every day make mistakes via short cuts and not caring. Home owners make mistakes via ignorance. Humans error. Why prefer one error over the other? The answer is simple -- Be smart. -- Test your work. -- Mix water + Dawn or Joy (they stick to the pipe) and wait for bubbles.
    – Paul
    Dec 9, 2022 at 2:59

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