Guide to Picking the Perfect Air Hose Fitting

An air hose won’t do much good if you don’t have the right air hose fitting. Today, I’m going to explain how to pick the perfect air fitting.1

– Consider the style of the fitting

You need to consider the style of the fitting. There are a number of differently-styled fittings and couplers, including everything from A-Style to T-Style.  Click here for a visual chart which identifies each type of fitting.

The most important thing you need to know about style is that you have to choose the same-styled plugs and coupler bodies to ensure a secure fit.

Some plugs – like A-Style – can only be paired with A-Style couplers. Other plugs, like A/M/T Style, accept all three most popular ¼ basic style plugs sold in the United States, including A-Style, M-Style, and T-Style.

– Other things to consider

Other things to consider when buying air hose fittings include:

-Maximum inlet pressure: The maximum pressure (in PSI) the air coupler/plug can withstand.

-Maximum temperature: Couplers may come with different temperature ratings. Typical maximum temperature ratings are 250 degrees Fahrenheit.

-Seals: NPT type thread seals are tapered and pull tight with fastened, creating a fluid tight seal.  Some include O-rings to increase the sealing power, while others do not. You can also manually increase the seal by adding Teflon tape or liquid thread sealant.

If your environment has unusually high pressure requirements or extreme temperatures, then be sure to pick a fitting suited to your unique environment.

– Check for NPT standards

NPT stands for National Pipe Taper. NPT is simply a standardization system. Air fittings manufactured to the NPT standard will have the same dimensional compatibility as air fittings made by other manufacturers.

That means you can easily swap out different fittings from different manufactures – provided they have the same dimensions and both are NPT standard. If that’s the case, then the parts will fit the same threaded hole in your actuator, air cylinder, air tool handle, valve, and any other applications where it may be required.

NPT standardization isn’t required when picking air fittings – but it certainly helps.

– Check for dimensions and sizing information

NPT size varies widely and can be kind of confusing. Here’s the problem: ¼” NPT fitting thread isn’t ¼ inch diameter. The actual diameter is closer to ½”.

Instead of memorizing the exact diameters of different NPT sizes, just consult the following chart:2

As you can see, 1/8” NPT size is equivalent to 5/16” diameter size and 2” NPT size is equivalent to 2 3/8” diameter, and so on.

Now, before you buy your fitting, you need to measure the diameter of the fitting. To do that, measure the diameter of the hole in inches. Then, take that number and compare it to the fractional sizes on the chart above, then choose the NPT size that pertains to that diameter. Done!

You can use this method to find the correct NPT size for female thread in a compressed air component, or any air tool handle, air cylinder, or valve.

Common NPT thread sizes include 1/8 NPT, 1/4 NPT, 3/8 NPT, and 1/2 NPT. Larger sizes are available, but these are the ones most commonly seen on store shelves.

How to buy compressed air fittings

Ram Products offers a full lineup of shop air hose and fittings. We offer A-Style, A/M/T Style, G-Style, H-Style, L-Style, M-Style, P-Style, and T-Style fittings – all of which are listed with their NPT sizing information.3

We also offer air hose and brass hose ferrules for your convenience. Order directly from for easy convenience. Or, contact your Ram Products sales representative today!

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