Planning a DIY gas fire pit? There are two common pipe thread standards used by the industry for gas fittings. It’s important to know the difference between the two, so you can select the right hoses and connectors for your fire pit.
In this guide, we’ll introduce you to the terminology; how to measure properly for parts (spoiler alert: the name size and the actual measurements, do not align); how to make proper connections; and testing for leaks. So, let’s get started!
Yes! There are two standard types of gas fittings used in the U.S.—NPT (National Pipe Thread) and “Flared.” The type of fitting used has nothing to do with whether your fire pit uses propane or natural gas, rather it has to do with the gas supply line or appliance.
GAS FITTINGS may have trace amounts of lead. Do not use for potable water!
As we noted earlier, there are two types of gas fittings used for DIY gas fire features. While they are very different from each other, you’ll often find that both types are used within one DIY fire pit project. That means you may be using couplers to go from one fitting type to the other. How they’re measured and how they make a seal is very different, so it’s important to have a good understanding of both types. The following information should help you keep things straight.
The most important thing to know about NPT fittings is that they’re tapered, and the seal is provided by compression in the threads. The more you turn them, the tighter the seal.
Since the seal is provided by the threads pressing against each other, it’s important to use yellow Teflon tape on the threads. NPT fittings require the use of this yellow Teflon tape because it is rated for use with gas.
When applying the Teflon tape, wrap the threads tightly by stretching the tape around the threads several times. The tape should be applied to the male end (exterior threads) of the coupler wrapping it clockwise when looking at the threads from the open end of the fitting. This will ensure that the tape won’t unravel when screwing the fitting in.
The second most important thing to note is that thread size does not equal pipe size. Gas pipe sizes are concerned with how much gas a pipe can deliver. For this reason, fitting sizes are loosely based on the inside diameter of the pipe. We say loosely because the inside diameter will depend on the material used for the pipe.
For example, an iron pipe has thicker walls than brass, so the inside diameter of the iron pipe will be smaller than brass. The thread sizes have to be a standard size in order for two fittings of different materials to be connected to each other.
While 1/2” NPT has an inside diameter of about half an inch (give or take), the actual threads measure 0.84”. Don’t worry, we’ll get into this later when we talk about how to measure gas fittings.
NPT is the most widely used thread for gas fittings in the U.S. When used with a proper joining medium (yellow Teflon tape or pipe compound), the tapered threads provide a solid mechanical connection as they conform to one another when tightened.
If you have to disassemble NPT fittings, it is highly recommended that you replace them with new fittings. The nature of the fitting is to compress the threads with force to create a seal. Once you have done that, the threads will now be deformed. It will be very difficult to recreate a tight seal with used parts.
Flared fittings are very different than NPT fittings and are commonly used for gas appliances. Flared fittings are easy to spot from their NPT counterpart, as the upper edge from the male fitting has a smooth angled tip. We call this angled tip the flare.
The female end has an inverted flare inside the fitting. When the two pieces are pressed tightly against one another, the flares coming in contact with each other creates the complete seal. No sealant is necessary with a flared connection.
The most important thing to know about flared fittings is that the threads don’t make the seal. The purpose of the threads on a flared fitting is to provide pressure at the tip of the fitting to make the seal. By pressing the flare tightly against the inverted flare, a tight seal is made. For this reason, you should never use Teflon tape on a flared fitting.
Never reuse a flare connector. Flare connectors are for one-time use only. Always replace the hose when disconnecting and reconnecting.
There are a lot of similar-looking terms used in the industry, and it can get confusing. Here are the most common terms you’re likely to see in regard to gas fire pits.
Adapter – Used to join two different types of pipe or fittings.
BSPT – Abbreviation for British Standard Pipe Thread, which is different than NPT.
Coupling – A short piece of pipe with female threads (interior) on both ends.
FIP – Abbreviation for Female Iron Pipe, this term is interchangeable with FNPT.
FNPT or FPT – Abbreviation for Female National Pipe Thread or Female Pipe Thread. This identifies a female NPT connection—threads on the inside.
BSPT (British Standard Pipe Thread) is the standard used in the United Kingdom and most of the world. BPST fittings are not the same size as NPT, so an adapter must be used to combine them.
MIP – Abbreviation for Male Iron Pipe, this term is interchangeable with MNPT.
MNPT or MPT – Abbreviation for Male National Pipe Thread or Male Pipe Thread. This identifies a male NPT connection—threads on the outside.
Nipple – A coupler with male threads (exterior) on both ends for connecting pipes.
NPT – Abbreviation for National Pipe Thread (or National Pipe Tapered Thread). Features tapered threads and are the standard used in the U.S. and Canada.
Union – A coupler that can be separated and repeatedly reassembled.
Measuring gas fittings is neither intuitive nor easy. This is because with gas we’re concerned with the volume of gas we can deliver to an appliance. You would think that we could base sizes on the inside diameter of the pipe, but we can’t do this because there is no standard material used for pipes. Different pipe material leads to slightly different sizes for the interior diameter.
The two most common metals used for gas pipes are iron and brass. Iron pipes require a wall thickness greater than brass pipes. So, to make sure the exterior measurement will be standard and fit into any other pipe or fitting, that means the inside diameter will be a tad smaller. That’s why we say the measurements are an approximation.
When measuring the size of your gas pipes, you should be measuring the diameter at the threads. Note: Your measurement will be significantly larger than the size name for the pipe.
Now, one of the most intimidating parts of the whole process for a gas fire pit DIYer, ordering the right size fittings. You now know that NPT and Flare size names do not correspond with the measurements you’ll take. With this knowledge, you can measure the fitting size by measuring the thread diameter and not wonder why your measurements are off.
For a quick reference, use the charts below to figure out what size you need. If you still have questions, please don’t hesitate to contact us. We want to help you avoid the frustration of getting the wrong part and having to reorder or make another trip to the store.
For additional information on how to measure pipe sizes, check out our article, “How to Measure Pipe Size.”
The good news is, if you can figure out the right size, parts should be pretty easy to find. The easiest of all? Ordering from the comfort of your home. Celestial Fire Glass carries many of the parts you might need, and we’re happy to consult with you in order to make sure you get the right part for your gas fire pit the first time around.
Another good resource would be to go to your local plumbing supply store. These stores are where contractors shop and will almost certainly have the fitting you need. You may find what you need at a big box store such as the Home Depot or Lowes, but if not, look to a more specialized hardware store.
PLUMBING SUPPLY doesn’t refer to just water – it also includes GAS plumbing.
As you might imagine, making the proper connections when building your fire pit is an important step. A leak is not only wasteful, but it can also be explosive and result in the loss of life.
NPT fittings require the use of yellow Teflon tape or pipe compound in order to get a proper seal.
Yellow Teflon tape, made specifically for gas fittings, helps lubricate the threads allowing for greater tightening, and also helps to fill in small pockets of air creating a tight seal. Other types of Teflon tape are not sufficient and should not be used. Pipe joining compound suitable for gas can be used in place of the yellow Teflon tape.
When using flared fittings, never join two or more connectors to make a longer connector. The connector/hose should be long enough to reach your burner in one piece, and without stretching or having tension.
Never use Teflon pipe tape or pipe compound on the threads of a flare connector. This will prevent the connector from bottoming out and making a proper seal.
There is no hard and fast rule around this issue because it partly depends on the quality of the parts, how tight you are able to get it with hand-tightening, and the materials the parts are made from.
You need to tighten enough to form a seal, but not so tight as to cause damage. As a general rule, you hand-tighten the fitting as far as you can, and then anywhere from 1-3 turns after that using a wrench.
You will likely need two wrenches, one to hold things steady and one to turn the fitting. Slowly turn until it seems like you aren’t making any more progress.
KEEP IN MIND, gas Fittings are NOT REVERSE-THREADED. The old saying, “Righty Tighty – Lefty Loosey” works with gas.
Do not jerk on the wrench abruptly, this gives you no control over how much you are tightening and does not allow you to feel what is happening.
Brass is softer than steel and if you go overboard with the tightening, it could break or crack the piece. There is less worry about breakage with a steel pipe, but it is possible to strip the threads if you tighten it too far.
It may be better to err on the side of less tight, test for leaks, and tighten more if needed.
It’s important to test your gas fire pit for leaks and luckily, there is a relatively easy and reliable way to do this. Combine 1 teaspoon dish detergent (which is designed to be sudsy) and 1 cup water in a spray bottle. If you don’t have a spray bottle on hand, you could use a small paint brush to slather it on the fittings. Coat all your fittings on both sides of the valve and regulator.
Then turn on the gas and look for foaming or bubbles. If you see bubbles, then you can try to tighten the fitting a little more and then test again.
WHEN YOU “spring clean” your fire feature, it’s a good idea to use the soapy water test to make sure your fittings and the length of your hoses are leak-free.
Creating a gas fire pit or fire table is a great DIY project, but sometimes there are elements that require a professional.
If you have natural gas, be sure to call in a licensed gas installer to set up your operation. While a small propane tank could certainly cause damage, it is minor compared to what would happen if you made a mistake while hooked up to a gas supply line with unlimited gas flow.
Nobody wants to take out a city block and their neighbors along with it. Call the professionals and let them make your gas fire pit safe by making sure the lines and connections have been constructed properly. You can find a local contractor by searching local plumbing companies.
For everything else, contact us! We’re here Monday through Friday, 8 a.m. to 5 p.m. ET. We enjoy talking with our customers and helping in any way we can. We’re located in Frederick, MD. If you find yourself nearby, stop in and say hello.
Understanding what port or straight thread vs. pipe or tapered thread fittings are utilized in and their design elements. This article describes the different types of fittings that are commonly used for high-end racing and street performance applications. The fittings we will discuss are Adapter Fittings (also called Standard, or Union), Port Fittings, and Pipe Fittings, as well as thread types and size standards associated with each.
Before we get into the types of fittings we’ll first define the thread types used on the fittings, as well as discuss applicable AN standards.
Thread Types:
Straight Thread - With straight thread the threads run parallel. Port Fittings and Adapter fittings using straight thread require use of an O-ring Boss Seal technique to seal against leakage. NPSC - American Standard Straight Coupling Pipe Thread are the standards for Straight Thread in the US.
Tapered Thread – Tapered thread, also known as Pipe Thread, typically uses a 2° angle on the threads (instead of running parallel). This allows the threads to interfere and seal off. Threads must be clean and precise, to make up for gaps between threads that allow for leakage. Pipe Fittings, which use Tapered Thread, don’t use O-rings, but rather must use compounds or Teflon Tape to help seal the threads. National Pipe Thread Taper (NPT) is a U.S. standard for tapered threads used on threaded pipes and fittings.
AN Standards High-end racing and performance fuel delivery systems most frequently implement fuel lines and fittings manufactured to AN Standards. During WWII the US military set specification standards for fasteners and fluid fittings used on military equipment. These standards are headed under “AN” which is the abbreviation for “Army-Navy", but is also known as "Air Force - Navy Aeronautical Standard". After the war many used surplus aerospace parts were used for racing, and thus introduced the AN standard into the racing and performance world. AN Standards as Applied to Fluid Carrying Tubes and Flexible Hoses In the case of tubes and flexible hoses used to carry fluid, “AN Size” designates the outer diameter of the hose or tubing in 1/16” increments. For example an AN size 2 designates a tube OD of 1/8” (2 x 1/16”), the tube OD of AN size 3 is 3/16” (3 x 1/16”). Note: The AN size number is correctly displayed with a dash before the number.
AN Standards as Applied to Fluid Carrying Fittings Each AN size also references a standard male and female thread size that is used on fittings - such as hose end fittings, adapters, and port fittings. This is known as “AN Thread Size”. AN fittings have Straight Thread, and use O-ring seals. The O-ring size is typically defined by the "AS" standard. Dash Numbers are typically assigned based on the size. Boss-Seal style O-rings are typically in the "900" Series. For example -906 is for -6AN ports, and -908 is for -8AN ports. AN Size and AN Thread Size Reference Chart The chart below references the tube (or flexible hose) OD and thread size for each AN size.
*Note: While these measurement s reflect AN standards, actual ID and OD can vary slightly from AN specification depending on supplier. BE SURE TO USE COMPATIBLE FITTINGS ONLY! Mismatched lines can come apart under pressure. Verify that inner diameters match!
Common Types of Fittings
Adapter Fittings Adapter Fittings – also known as Standard Fittings or Union Fittings – are commonly used to connect fuel line tubes and hoses to fuel pumps, fuel regulators, and fuel filters. While Adapter Fittings are available in SAE size configurations, most high-end racing and performance fuel systems use those manufactured to AN standards (document AN815, defines standard union fittings). With AN versions, the fitting ends typically use a 37° cone on each end (as per Military Standard MS33656). AN standards dictate use of Straight Thread for Adapters, requiring use of O-rings. Special port machining is done to "capture" and properly compress the O-ring, as too much stress can damage the O-ring, and too little can cause leakage. These port standards are designed to precisely "load" the O-ring automatically during installation. Use of The O-ring seals allow for greater sealing ability with very high reliability of installation as compared to Tapered Thread using sealing compounds or Teflon tape.
Pipe Fittings Pipe Fittings can be used to connect fuel lines to the port on a fuel pump or fuel pressure regulator, as well as connect fuel pressure gauges to gauge ports. One end (the port end) of the fitting can be described as a male open-ended cylinder with Tapered Thread (also called Pipe Thread) on the outer diameter. This fits into a female port of corresponding size and thread pitch. The other end typically uses a 37° cone and Straight Thread. The Tapered Thread on the port end of the fitting must use sealing compound or Teflon tape to help avoid leakage. However, in high-pressure fuel system applications this method has proven more leak prone than the O-ring seal method used with Straight Thread fittings. As well, Teflon tape has the potential to leave debris in the fuel systemWhich leads us to the description of Port Fittings.
Port Fittings Port Fittings (also known as O-Ring Base or ORB fittings) function just like Pipe Fittings, but with the following distinctions. Port Fittings conform to AN standards - typically per Military Standard MS33649. The cone end uses Straight Thread and a 37° cone. The male port end of the fitting uses Straight Thread, and is received by a female port of corresponding size and thread pitch. Port Fittings require use of O-rings. Like AN Adapters, special port machining is done to "capture" and properly compress the O-ring which allows for greater sealing ability with very high reliability of installation as compared to Tapered Threads using sealing compounds or Teflon tape. This reliability makes Port Fittings the preferred choice over Pipe Fittings for high-end racing and performance fuel system applications. It should be noted that while manufacturers of high performance fuel delivery systems often specify Port Fittings for connections to fuel pumps and fuel pump regulators, the connections to fuel pressure gauges, via gauge ports, most often utilize Pipe Fittings. This is because the vast majority of the in-line fuel pressure gauges on the market use Pipe Fittings for connection.
We hope this overview has provided a better understanding of the differences and uses of Straight Thread versus Pipe Thread, as well as the types of fittings used. If you have further questions about fuel delivery system plumbing, please contact Fuelab Technical Support.