Different Types of Air Hose Fittings – 3/8 Quick Connect Air Hose Fittings


    Air hose fittings come in many different sizes and colors like the 3/8 quick connect air hose fittings and numerous others. In this post we will discuss about different kinds of air hose fittings.

    On the exterior, most couplers appear the same, therefore let us start with plugs.

    3/8 quick connect air hose fittings

    Plugs_3/8 quick connect air hose fittings

    To begin, there are several fundamental flow sizes, such as 3/8 quick connect air hose fittings, 1/4′′, 3/8′′, and 1/2′′. This does not relate to the size of the fitting on the plug's end, but rather to the amount of air that the plug can handle. For our purposes, we will focus on 1/4′′ basic flow size fittings, since this is the size that you would encounter in most residential and light business applications.

    In the 1/4′′ basic flow size, you are likely to come across either industrial or automotive plugs. They are the ones you will find at large box shops like Home Depot and Lowes. ARO plugs in the 1/4′′ basic flow size are also available. For bigger fundamental flow types, such as G-style for the industrial, there are various industrial, automotive, and ARO plugs, but we will not get into that here.

    Industrial Socket:

    An industrial-style plug is seen above. They are known by many distinct names. For example, this may sometimes be referred to as a Milton plug, although it is more properly referred to as a Milton M-style. It is sometimes referred to as type D or I/M style.

    To add to the confusion, Milton has a D-style plug that is not always compatible with this type.

    High Flow Plug vs. Industrial Plug:

    The V-style plug is a high flow style plug, similar to an industrial type connector, but with a wider aperture to allow more airflow, as seen above. The pictures above show a Milton V-style high flow plug, although other firms manufacture high flow plugs as well.


    There is a coupler for each of the various connectors. If you have that particular coupler, it is likely that it will only take plugs of the same type. Although I discovered that certain industrial-only type couplers can take V-style connectors, I would not put my money on it.

    The issue is that most couplers appear the same on the exterior, making them more difficult to detect than plugs. There is a fairly recognized method of recognizing them by counting the number of thin and thick "stripes" on the body of the coupler, although it is mostly ineffective since not everyone follows it.

    Also, unless you have two couplers from the same manufacturer, one company's thick stripe may seem to be the same as another company's thin stripe. Furthermore, you must know which marks are certain styles, because the plugs do not have matching markings.

    There are also universal couplers. Some say that they only work with industrial and automotive plugs, while others claim that they work with industrial, automotive, and ARO plugs as well.

    The Milton V-style coupler is another option. It is intended to be the Hi-Flow plug's high flow companion. According to Milton, they are also intended to accommodate A, T, and M type plugs (ARO, automotive, and industrial plugs, respectively).

    Another company's high flow coupler would take automotive and industrial connectors, but that was in stock and not under pressure. I do not want to file a claim if I can not locate supporting documents.

    I have also heard that certain universal couplers are less dependable than single-style couplers — that they are more prone to leakage, particularly when sideways pressure is applied to the plug.

    Universal Couplers and M Style Couplers - 3/8 quick connect air hose fittings

    Another advantage of couplers is that they may be manual or automated. Looking at the picture above, you can see the difference: the automated coupler has the sleeve pulled back when no plug is entered.

    A manual coupler requires you to draw back the sleeve to enter the plug and establish the connection, while an automated coupler requires you to just put the plug into the coupler and it will connect automatically. To remove the plug, you must still pull back the sleeve on both kinds.

    Only universal and V-style couplers are available in automated forms, as far as I can determine.

    Color-Coded Connections 3/8 quick connect air hose fittings

    Several manufacturers, realizing how perplexing the numerous various kinds of connectors and couplers may be, have implemented a color-coded scheme.

    • The color of industrial (M-style) is red.
    • The color of ARO (A-style) is green.
    • Blue is the color of automobiles (T-style).
    • Purple is the color of the V-style.
    • ColorConnex air line connectors are available in a variety of colors.
    • Legacy features a system called ColorConnex.
    • The color of industrial (Type D) is red.
    • Blue is the color of automobiles (Type C).
    • The color of ARO (Type B) is green.

    One benefit of adopting Legacy's color-coded method, according to Legacy, is that you can easily differentiate between oil-free and oily lines. If you are going to use a paint sprayer, you do not want a hose with residual oil in it, therefore you could choose green for all paint spraying equipment and red for anything else.


    So, what is the key lesson from all of this? You are most likely utilizing automotive or industrial type connectors and couplers. If you want to be safe, get a universal coupler, and you should almost never have a connection issue.

    If you want to be completely secure, my advice is to go with a more recognized manufacturer's fittings, ideally, one that you can purchase locally so you can easily replace a coupling if necessary - either that, or make sure you have a few replacements. I hope that this post will help you in picking out the best hose fitting for you. 3/8 quick connect air hose fittings is a universal fitting for many.

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