What are AN Fittings and Adapters?


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AN(Army Navy) fittings and adaptors are used to connect flexible hoses and fluid-carrying metal tubing together.

AN stands for Army-Navy.

AN fittings are a particular type of fitting used to connect flexible hoses and fluid-carrying metal tubing together. The name is derived from a standardized joint agreement between the Army and Navy during World War II regarding the size specification of the fitting. A-N, therefore, stands for Army-Navy.
AN fittings, also known as AN threads, were originally used in the aerospace industry and were hence designed to meet very strict performance standards relating to aeronautics. As these fittings were later adopted for various land and sea applications, confusion started occurring between AN fittings and their industrial counterpart, SAE 37° fitting.
AN fittings make use of a 37° flare for the sealing surface. It is important to remember not to use AN fittings with different flare-type fittings, as this will most likely lead to fluid leaks and subsequent damage to the fittings.

AN Thread Sizes

AN fittings range in size from -2 (dash two) to -32 in irregular steps that each equates to the outer diameter of the tubing. The outer diameter of the tube or hose that each fitting is to be used for is correlated with the inner diameter of the fitting itself.

The table below lists the size specifications of AN fittings ranging from dash-two to dash-thirty-two, along with the corresponding SAE thread sizes.

Table showing AN size, Hose inner diameter divided by Tube outer diameter, and SAE Thread Size

What Are AN Adapters?

While AN fittings are used to connect tubing together, adapters are designed to connect two different sizes or types of fittings together. These are very important tools in plumbing and hydraulics as they allow for the interchange of different standards of components.
Since we aren’t lucky enough to have a single standard, sometimes one is forced into joining components of different standards to one another. This could be a metric hose end and a BSPP fitting, which would require an adapter to join together.
Adapters can also be used to join plumbing together or split plumbing apart. Moreover, as mentioned, adapters can also be used to attach different-sized components together. Allowing fluid interchange from one diameter fitting or tubing to another will always require an adapter.
Sometimes, the terms fittings and adapters are used interchangeably. However, there is no doubt that they are used for different functions.