What are AN Fittings and Adapters?

Introduction to AN Fittings

AN fittings are the industry's top choice of high-performance metal fittings. AN is Army-Navy, a fitting developed by the military for use on aircraft. These are precision manufactured to fit comfortably to give ease of fit with an excellent seal to eliminate the risk of damage from over tightening.

Instead of a tapered thread, AN fittings utilize a 37-degree sealing face to ensure a positive seal. This flare style hose connections system ensures a good seal and will not crack and can be removed and replaced so that you can reuse the hose and fitting on other high performance applications and installations. All the components are interchangeable with other vendors as well so you can mix/match to make the line what you need and you know they will work the first time if you ordered from another supplier. From being used for brake lines to air conditioning and high pressure fluids, AN fittings are set to perform in any application.

What Are AN Adapters?

AN adapters are the primary method used to adapt AN fittings to multiple thread types and sizes and flare configurations. These adapters are designed to connect between AN and a variety of other thread systems with the least resistance to flow possible in the connection of performance parts.

The most common application for adapters involves connecting AN fittings to NPT (National Pipe Thread), as many automotive and industrial parts use NPT threading. AN to NPT adapter fittings allow the superior sealing characteristics of AN connections while maintaining compatibility with standard threaded ports.

Another critical category is bulkhead adapters that provide protected fluid passage through panels, firewalls or enclosures, with integrity. Valve cover adapters are less prone to leak under vibration and thermal expansion.

Types of AN Fittings

Straight, 45-degree, and 90-degree fittings

Hose end fittings are available in multiple configurations for various routing requirements and space constraints. Straight fittings are the most direct route connecting point A to B, and require more room for routing the hose line.

45-degree fittings provide a perfect blend of flow and flexibility, keeping the angle to a minimum, and allowing the hose to be arranged and bent, but not enough to restrict the flow. These fittings are widely used in fuel systems where bent tube type fittings are ineffective.

90-degree fittings enable sharp direction changes in tight spaces, though they do introduce some pressure drop due to the flow direction change. These fittings are essential for connecting flexible hoses in confined areas where straight routing isn't possible.

Bulkhead fittings

Bulkhead adapters assure a leak-free flow of fluid lines through barriers without jeopardizing system pressures. These rigid fittings have threaded bodies which install on panels using sealing washers or O-rings to prevent leaks around panel mounting holes.

Reusable vs. crimp-style fittings

The re-usable fittings can be re-fitted in the field and does not require a crimping machine to be replaced. These fittings make use of a mechanical compression to the hose, with proper assembly being of critical importance for dependable operation.

Crimp-style fittings provide permanent attachment between the fitting and hose, offering superior strength and reliability for critical applications. Professional crimping equipment provides for consistent, repeatable terminations that meet or exceed manufacturer specifications.

Swivel vs. non-swivel fittings

Rotating swivel fittings feature a rotating mechanism allowing the hose to rotate independently of the fitting body to eliminate any induced twist to the hose and ease installation, addressing thermal expansion or vibration related movement. This configuration eliminates hose twist during installation and in use.

Non-swivel fittings provide a direct, unrestricted flow and are typically stronger than swivel fittings. Where hose routing is fixed and additional hose length is not required, non-swivel fittings may be used to eliminate a potential leak point. Because of their less complicated design, these fittings are rated at a little bit higher pressure levels.

Vacuum fittings often benefit from swivel designs, as vacuum systems may experience significant thermal expansion that could stress rigid connections. The ability to accommodate movement extends system life and maintains vacuum integrity.

AN Adapters Explained

Purpose of adapters in plumbing or fuel systems

Adapters enable integration of high performance AN connections into systems utilizing different thread standards or configurations. In automotive fuel systems, adapters allow connection of stainless braided hose assemblies to factory fuel rails or pumps that use NPT or metric threading.

Common adapter types (AN to NPT, AN to ORB, AN to metric)

AN to NPT adapter fittings are the most common types and they mingle AN threads with NPT threads. These adapters will work with all the various sealing methods used by the various manufacturers, including the AN flare sealing and the NPT thread interference sealing method.

AN to ORB (O-Ring Boss) adapters are used to access components that need a sealed connection, typical components include fuel lines & tanks, radiators, hydraulic systems on motors, pumps, and cylinders, most popularly in air conditioning and automotive power steering systems. When properly installed and when used with O-ring compatible materials, O-ring seals are very reliable.

Metric adapters enable connection to European and Asian components that utilize metric threading standards. These adapters will retain AN performance, while having the tolerance for thread pitch diameter and length of hex in metric systems.

Thread compatibility and sealing considerations

Thread liner compatibility is not only a matter of matching diameters. The thread pitch, engagement, and sealing method all must be taken into account. AN threads are machined to a specific pitch and 37-degree flare angle that have to be maintained on the entire connection.

Sealing considerations account for the fact that different methods are employed for different types of threads, such as AN using metal-to-metal flare sealing, NPT using thread interference, or metric types that are frequently supplied with O-rings or other sealants.

AN Fitting Sizes and Identification

How AN sizing works (e.g., AN-6 = 6/16” = 3/8”)

AN sizing utilizes a dash number system based on sixteenths of an inch, with AN-6 representing 6/16" or 3/8" inside diameter. This standardized sizing system ensures consistent bore sizes across different manufacturers and component types.

The outer diameter of the tube or hose typically exceeds the dash number size due to wall thickness, with the inside diameter matching the dash number specification. Understanding this relationship is crucial for proper hose selection and flow calculations.

Measuring and selecting the right size

Sizing is accomplished by measuring the inside diameter of the tube, or calculating required flow for new systems. Velocity calculations for proper sizing of various fluid types and system requirements.

To measure existing connections, you must determine the thread pitch and diameter - which generally can only be done accurately with thread pitch gauges. Initial size estimates can be made by visual examination, although accurate measurement tools facilitate component selection.

Common size applications (fuel lines, brake lines, oil systems)

AN-6 and AN-8 fittings were the norm for fuel system applications, where AN-4 was used for return lines and smaller connections. High flow applications will require AN-10 or greater size to reduce pressure drop and maintain sufficient fuel delivery.

In brake systems, AN-3 up to the individual caliper/wheel connection is great and AN-4 to main lines gives just enough flow without being too bulky. The high pressure design of the fitting makes it ideal for high performance brake applications.

Oil systems often employ AN-10 or AN-12 fittings for main supply and return lines, with smaller sizes used for pressure sensing and auxiliary connections. The temperature resistance of quality AN fittings ensures reliable operation in high-temperature oil systems.

Advantages of Using AN Fittings and Adapters

The biggest benefit of AN fittings is that they seal and don’t leak when installed in hot, high pressure areas such as in the engine bay. The 37-degree flare fitting is a reliable connector that is resistant to corrosion and can be connected or disconnected repeatedly without loss of sealing effectiveness.

A standardized approach in the aerospace industry provides interchangeability and equipment availability to the fittings of different manufacturers meeting the identical thread requirements and sealing principles. Standardizing minimizes inventory and design requirements.

How to Install AN Fittings and Adapters

Required tools and equipment

Proper installation requires specific tools including AN wrenches sized for the particular type of fitting being installed. These wrenches are machined to fit aluminum or steel fitting surfaces without causing damage, and to achieve a secure fit.

Thread pitch gauges help verify compatibility before installation, preventing cross-threading or incorrect component selection. Proper measuring tools ensure accurate sizing and thread identification for both new installations and replacement applications.

Step-by-step assembly instructions

The first step is to ensure that the thread patterns match and that each part fits the size of your piece as needed. All threads and sealing surfaces must be clean in order to avoid imperfections, which can prevent tight closure or lead to early breakage.

Coat threads and sealing surfaces with suitable assembly lubricant, not exceeding applied thickness which could otherwise be a source of contamination of the fluid system. Tighten components finger tight until flare faces contact, use wrenches to reach final torque.

Common mistakes to avoid

Cross-threading stands as the most-likely installation error, typically caused by component misalignment or over installation. A little bit of extra time spent ensuring the threads are engaged will save your components from costly damage.

Over-tightening aluminum fittings can strip threads or damage sealing surfaces, later leading to leaks and failures that are not visible to the eye. Following manufacturer torque specifications for reliable sealing without component damage.

Using incompatible thread types or sizes creates unreliable connections that may fail under pressure or vibration. Proper identification and verification prevent these potentially dangerous installation errors.

How to Choose the Right AN Fittings and Adapters

Choosing the appropriate hose system starts with the proper identification of existing components and requirements, such as thread types, pressure ratings and temperature ranges. If the specific application is understood, choices of the components are narrowed down. The material of construction is dependent on the compatibility of the fluid and atmosphere, and the choice is between stainless and aluminum, depending on your requirements.

Conclusion

AN fittings are the highest performing fittings, providing unmatched reliability and performance in demanding applications. From their origins in World War II aerospace applications to modern racing and industrial use, these precision components continue to set the standard for critical fluid system connections.

Knowing how to choose, install, and maintain AN fittings are an important part of any system that lasts. Whether plumbing a fuel system or connecting hydraulic lines, we can rely on the superior sealing and interchangeability of AN components to give us certainty that the system will function as it should.