June 05, 2023 / by Danny Mavis

While anyone can get carried away fitting forged internals or faster spooling turbos, it’s the minor parts that connect different engine components -hoses and fittings – that get overlooked in almost every engine upgrade. Stock components aren’t designed to be adaptable to abrupt changes in pressure and temperatures as in seen in heavily modified engines, and the factory fittings are the first to give way. These can cause serious issues such as leaking brake fluid and fuel, and is what you’d least expect when out on the track. 

For that purpose, any upgrades to brake and fuel lines, the power steering plumbing or oil cooling systems should be followed up with bespoke fittings. The industry standard today is the little-understood AN fittings. Let’s delve deeper into what these fittings are, why you want them in your car, and the benefits they bring.  

What are AN Fittings?

AN, or Army-Navy fittings, are essential components in different fields, but more so in the automotive (and by extension, motorsports) and aerospace industries. Each fitting is a unique design, with a 37-degree flare at the end, and this allows for a secure connection of hoses, void of possible leaks. The fittings are offered in a range of sizes and shapes to suit different applications. And they are worlds apart from stock engine fittings made to price points that hurt both performance and longevity.  

an fittings for car
source: summitracing.com

Where They’re Used

These types of fittings developed from the strict performance requirements of military vehicles and aircraft used by the US forces in WWII. Since then their indestructible nature has proven to be a boon in demanding aerospace, industrial, and other areas where lightweight and high-pressure connections as well as high flow rates are critical. In this sense, they have also been adapted to bring the ultimate performance in different vehicle systems, where they provide a sealed connection that is much better than traditional factory push-on nipples and hose clamps. 

The fittings are made of high-grade 6063-T6 billet aluminium or stainless steel, and the 37-degree flares allow for a sealed metal-on-metal connection. They are used in vehicle oil cooling systems, specifically in plumbing hoses that circulate the oil, in high-performance fuel lines to deliver adequate fuel at high pressure, and in braided brake lines to supply sufficient stopping power. Other racing applications of AN fittings are in power steering plumbing to allow easier and faster changes of direction and the right boost and cooling in different types of fittings found in turbocharging components.

Why Have AN Fittings in Your Car? 

In high-performance racing, any leaks in hoses, lines or connections supplying fluid to different systems not only hurt performance or result in engine failure but can easily become a safety trap. Lines with the proper fittings and adapters are meant to last the extremes engines and vehicles undergo when pushed hard, They are subjected to high temperatures, pressure, vibration and chemicals and yet are durable enough to resist any kind of wear and tear. 

hose and fittings
source: dragzine.com

The fittings are also easy and quick to get on and off hoses, and for racing uses, speed is essential both on and off the track. Being easy to install and assemble also means that they are different sizes and fitting types, as well as adaptors in connections relying on dissimilar diameters. 

Getting a Grip with AN Fitting Sizes

Sizing the fittings right is one area where most newcomers stumble. AN sizing can be confusing at first, but you should be able to tell the size of the fitting in no time. This refers to the outer diameter (O.D.) of the hose and is stated in 1/16th of an inch increments. Each AN size also has its own standard thread size. For example, a -4 AN fitting, like something you’d find in fuel lines, has an outer diameter of 4/16ths or a 1/4  of an inch. And -8 AN hoses often seen in coolant and oil cooling systems are actually 8/16ths or half an inch in outer diameter. 

Fitting Types, Hoses and Adaptors

There are 3 basic types of AN fittings used to connect hoses in racing applications: crimp-style fittings that offer the most reliable seal, with hoses crimped using hydraulic presses and dies; reusable hose ends, consisting of a two-part system and commonly found in braided and nylon lines and hoses, and simple push-lock fittings seen with coated hoses and used where assembly speed is necessary. 

hose fittings
source: enginelabs.com

Each type is meant to be used with the appropriate AN hoses. These have inner walls made either of rubber, polyethylene or Teflon, with outer braided steel or nylon casings. The aim is to handle different types of fluids faced with temperature, pressure and abrasion extremes. 

AN adaptors are the parts that connect AN hardware to the appropriate engine components. They can come in varying angles, from straight, as well as 30, 45, 60, 90, 120 and 180 degrees. The aim is to provide a smoother run for the fluid or gases with minimal restrictions. And they come in different shapes, including tees and elbows. Typical types are bulkhead fittings, breather adaptors, O-ring boss fittings, sensor flow bypasses, brake booster valves, turbo drain adaptors and more.