Air Hose Fittings Types

Air Hose Fittings Types

The most mind-boggling part of using air tools is navigating through the different air hose fitting types. These tiny parts may not seem like a big deal, but they have to be changed so that your air tool works properly.

Once you’ve figured out which one goes with which, you can switch between tools swiftly.

But if you’re new to this, where do you start?

Flow sizes, styles, airflow/connection category all correlate to an air fitting’s use. In this article, we’ll be going through these basic differentiations as well as a step-by-step guide to demonstrate how to change a fitting.

Before we get into all that, let’s start with getting to know the air hose fittings types.


What are Male End Fittings (Plugs)?

Quick couplers consist of two components – the plug and the socket. The plug is the male end of the coupler which is screwed onto the end of the air tool of your choice.

On the other hand, the socket is the female end which is connected to the end of the air hose.

Basic Flow Sizes

Just like all air hose fittings, plugs also come in assorted sizes.

You might have seen ½”, 1”, ⅜”, and ¾” being used to describe these plugs. These numbers are commonly misunderstood to be the size of the plug itself, but they’re actually the flow size.

The flow size tells us the volume of air the plug is able to withstand. Depending on each flow size, you can find a number of different air compressor hose fittings types. This also applies to plugs.

Styles and Names

Plugs come in various styles, categorized into industrial or automotive types. These plug types include: ARO, V-Style, Lincoln, and more.

Also, these styles may come in alternative names. For instance, an ARO plug is also called a Milton M-Style plug, type D style plug, or I/M style plug.


When discussing air compressor fittings quick connect, couplers play a huge role in establishing a secure connection for the air tool to function properly. Each plug type has its corresponding coupler.

As with plugs, couplers also come in styles such as ARO, V-Style, Lincoln, etc. Every coupler will only accept the plug of the same style. This can be a problem as most couplers look identical to one another, and are hard to pair with their complementary plug.

However, there are universal couplers that go with most plugs.

Couplers are more convenient to use than standard threaded fittings as they make switching between air tools quicker. This enables you to swiftly move from task to task, and makes your work streamlined.

We can break down couplers into three main categories: style, basic flow style, and connection type. Here’s a quick rundown of each of these sections –

a. Style

There are 10 main styles of couplers that are widely available in the market. They include L, A, D, M, T, AA, H, P, G.125”, and G.375”. These styles differ by their SCFM rate.

So, for instance, the A type coupler moves about 34 standard cubic feet of air per minute, while the G.375” type moves about 99 SCFM, making it a more powerful coupler variation.

For heavy duty pneumatic tools, it’s best to go for couplers that support a high SCFM rate.

b. Basic Flow Size

There are only three basic flow sizes for couplers – ¼”, ⅜”, and ½”. The “basic flow size” refers to the air handling capacity of the coupler.

To put it simply, ¼” are couplers up to 40 SCFM, ⅜” are up to 60 SCFM, and ½” are 60 SCFM and up.

c. Connection

The most common coupler connection type is the NPT type, which is a female and male pipe connection.

There are also hose barb type connections which are installed by pushing them into a pipe/hose, instead of being threaded as with the NPT type.

Why are Couplers and Plugs in So Many Colors and Materials?

When identifying couplers, it’s recommended to not focus on the manufacturer but the style of the coupler. This is because most manufacturer labels will try to put as many unique styles as possible to diversify their range of products, which makes it very confusing to differentiate between couplers.

For example, take an M style plug from Milton and an M style female coupler from Errol. You will notice them connecting without any trouble as they are of the same style, which disproves the misconception that couplers have to be from the same manufacturer.

Color-Coded Couplers and Plugs

So how do we identify the various styles of air compressor coupler types? Sometimes, they are color-coded and denoted.

Brands such as Milton have come out with the ColorFit system which makes it easier for their consumers to match plugs with their corresponding couplers. For Milton, the color chart is as follows: red for industrial type, blue for automotive type, green for ARO, and purple for V-style.

Different Designs and Materials of Air Fittings

Couplers and plugs can also be found in a variety of different materials and designs.

The variety of air fittings types include: metal bar couplers, plastic coupler and plug, and couplers with ball bearings. Even though these are different from one another, they all share the same purpose of preventing leaks and providing a steady flow of air.

Fittings are found in different designs and materials for efficient conductivity, flow of air, and use. For various purposes, you may require a coupler or plug of a different design/material than the usual metal one.

Take a Plastic push in fitting, for example – it’s not as strong as a brass or stainless-steel fitting, but it’s best for light pneumatic tools.

Air Fitting Type Chart

To identify unknown air fitting types, Milton recommends using their plug identification chart, as shown here –

Air Fitting Type Chart
Air Fitting Type Chart

This chart consists of all the available air fittings types. Put any plug up to the chart and you’ll easily be able to identify which style it is. As we’ve already discussed, couplers will only accept plugs that are of the same style, except for universal couplers.

So, once you’ve identified the plug style, you’ll be able to identify the coupler style as well – given that the plug fits easily into the coupler.

How are Air Hose Fittings Measured?

Air hose fittings, or couplers, are measured according to three categories – style, basic flow size, and SCFM rate. This chart shows the flow size and SCFM of each coupler style –

Coupler StyleBasic Flow SizeStandard Cubic Feet of Air Per Minute (SCFM rate)

How to Connect Air Hose Fittings

Now that we’re familiar with all the air compressor fittings quick connect and their differences, it’s time to put the info into a practical demonstration. Air hose fittings are very simple to install, so you’ll get the hang of it after your first try.

For the following guide, we’ve chosen the Nitto style type as an example. Here are the steps to installing an air hose fitting –

Step 1 – Select the Correct Hose Fitting

If you already have a fitting installed, take a good look at it to determine which fitting you will need that will support the pneumatic tool of your choice. In this case, we are using the Nitto style fitting as shown in the picture above.

Remember – the female end is going to be fitted onto the hose end, whereas the male end is fitted onto the tool. So for this one, there’s going to be a fitting on the hose end, a fitting on the end of the pneumatic tool, and a female fitting between them. This will be shown clearly at the final step.

Step 2 – Use Teflon Tape to Seal the End of the Air Hose

You can use teflon tape, thread tape, or sealant paste on the male end of the air hose to make sure all the gaps are sealed. Even though the fittings are leak proof, it’s good to prevent any possibility of the air escaping through gaps or loose ends.

Step 3 – Adjust the Female Fitting onto the Air Hose End

Now, take the female fitting and screw it onto the male end of the air hose. The fitting has to be secured tightly or it could end in a number of mishaps, such as air leaks, bursts, or even injury. Take a spanner and wind the fitting until it is tightly put into its spot.

The plug, or the male end of the fitting, should be adjusted on the end of your air tool to connect with the female fitting. Make sure you use the corresponding plug on your pneumatic tool and that it’s screwed on tightly.

Step 4 – Connect the Air Tool

Connect the pneumatic tool to the air hose fitting. The plug should easily slip into the coupler. With the Nitto style fitting that we used, there’s a twist to lock feature which secures the fitting in place. If you’re using a different style fitting, make sure it is secured tightly by tugging on both ends of the hose and tool.

Test out the tool and check to see if there are any air leaks. Most of the time, you can hear a whining sound. If this is the case, take apart the fitting and reinstall it using more sealant tape or paste around the problematic areas.

How to Connect Two Hoses

If you don’t already have a fitting installed into your air hose, this is what you need to do –

Step 1 – Adjust Pipe Clamp

Pick a barbed fitting of the correct size, according to the diameter of the opening of your air hose. Before you put on the fitting, you will have to adjust the pipe clamp. This pipe clamp also needs to be the right size. If the pipe clamp fits, it should go around the hose easily without getting snagged or coming off.

Make sure the clamp is secure with a wrench or spanner.

Step 2 – Put on the Fitting

Now that the clamp is adjusted, take the fitting and push it into the hose opening. Make sure the inner bit of the fitting is completely inside the hose so that the outer part sticks out. Once the fitting is in, push the clamp upwards so that it holds the sides of the hose around the fitting tightly.

Step 3 – Secure the Clamp Around the Hose

To make sure the fitting or hose doesn’t come loose, tighten the clamp with a spanner or wrench. This will prevent any mishaps such as air leaks or bursts. When tightening the clamp, make sure to use the correct tightening tool.

Assess the clamp and how it fits around the hose – if it’s secured properly, you should see an indentation on the hose. Some people make the mistake of having a short edge of the hose under the clamp, which leads to bursts. To prevent this, make sure the hose is touching the bottom of the outer part of the fitting.

Step 4 – Connect Another Hose to the Female Fitting

To extend the length of the hose, we’re going to adjust another hose to the female fitting that we have just installed. For this step, you will need to repeat steps 1 through 3 but with a male end fitting instead of a female one.

So again, put on a pipe clamp, push in the inner part of the male fitting into the hose, push up the clamp, and secure it around the fitting with a wrench.

Step 5 – Connect the Two Air Hoses Together

Finally, you should be able to connect the two air hoses together. The male fitting should slip into the female fitting, and lock in place. Test out the hose and check to see if there are any leaks or loose ends around the fittings. If you spot any problematic points, take apart the fitting and reinstall it using teflon tape.

If you’re struggling with a step, or need a clearer demonstration of this guide, you can refer to this video tutorial.

YouTube video

Frequently Asked Questions

1. Should you use Teflon tape on air fittings?

Teflon tape, thread tape, and sealant paste are some of the most used options for securing an air fitting. When air fittings come loose, have gaps between the clamps, or the hose has small tears, these sealing materials are used to prevent further air leaks.

Even though it’s completely fine to not use teflon tape on air fittings, we recommend doing so to reduce the possibility of mishaps from occurring.

2. Can you connect two air hoses together?

Yes, it’s possible to connect two air hoses together. First, you’ll need to install a female end fitting to one end of a hose, and a male end to an end of a different hose. Once these two fittings are put in place tightly, you can easily connect them.

For more details on how to do this, check out our How to Connect Air Hose Fittings – Connecting Two Hoses section.

3. What is the most common air compressor fitting size?

The most common air compressor fitting has a basic flow size of ½” or ¼”. ¼” fittings can produce anywhere between 32 SCFM to 40 SCFM, whereas ½” fittings go even higher, up to 99 SCFM. ½” fittings are commonly used for high powered and heavy-duty pneumatic tools, while ¼” fittings are used for light work.

4. Are air compressor fittings universal?

There are a few universal couplers that can be found in the market. However, most couplers are of a specific type. These couplers are very finicky to deal with, as they only connect to plugs of the same style. To know more about the different styles of air fittings, check out our chart in our How are Air Hose Fittings Measured? section.

Air compressor hoses on the other hand are universal. Most air compressor hoses share the same purpose of connecting the compressor itself with the pneumatic tool, and providing air to pass between them.

5. What is the difference between automotive and industrial air fittings?

Automotive and industrial are the two main types of couplers. The difference between the two types can be found in their appearances. Industrial style couplers have two stripes across the fitting, while the automotive has one stripe.

As for the plugs, the industrial style one is much longer than the automotive one and also has a differently shaped head.


The main takeaway from our guide should be to not let the plethora of air hose fittings types on the market overwhelm you. Both the charts we’ve given cover the basic types with their most common names, if you remember these, then the alternative titles won’t phase you.

When following our step-by-step guide, make sure to prioritize any installation manual (if you are given one) before our information.

We use the Nitto style fitting as an example, but other fittings may require a different approach. So, keep in mind the specific fitting type you’re working with and install it accordingly.

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