Mark Houlahan
Brand Manager, Mustang Monthly
January 27, 2014

Fluid transfer is a critical part of your Ford's underhood operations. From cooling the engine to providing the necessary fuel to your carburetor or EFI system, using the proper hose material and fluid fittings, as well as the correct assembly techniques, is critical to ensuring passenger safety and proper vehicle component function. Taking short-cuts can lead to immediate and expensive engine damage, or even a total loss of your Ford due to fire or accident caused by the loss of vital engine fluids like gasoline, transmission fluid, and more.

Many people like the look of AN hose and fittings, yet are unsure of the proper hose type to use for a specific fluid, nor do they understand how to properly assemble AN hose and fittings together for a safe and solid connection. There are several hose types available and using the proper hose for the application is not only critical to the life of the hose, but it can also cause failure of the component the hose is attached to. The same can be said for end fittings. End fittings are available in steel and aluminum and in a dizzying amount of sizes, angles, and colors.

AN hoses and fittings are as tough as they look. They can take much more abuse than a stock rubber hose, have much higher operating pressures, and their threaded fittings allow quick removal of components. We've all had to deal with a brass hose barb fitting and a rubber hose that is practically welded to it (which usually entails cutting the hose off with a razor blade). The threaded end fitting on an AN hose eliminates such hassles and allows easier servicing and inspection; a must for race cars and a nice feature for performance street vehicles to have as well.

The AN specification is actually a military spec that dates back to World War II. It is a joint standard that was used for both the Air Force (not the Army, according to Parker's Tube Fittings Division) and Navy (hence the AN term) for fluid transfer fittings—think fluid lines on airplanes. Called the Parker Triple Fitting, these fittings were originally designed by Parker in the early 1930s as a replacement for inverted flare fittings (common to automotive brake lines) that were leaking due to the higher pressures seen in aviation. The ease of line assembly made AN fitting use popular. The Parker Triple Fitting was the forerunner of the modern AN fitting, as it used a 30-degree flare. Today, all AN-spec fittings feature a 37-degree flare. There remains some confusion regarding the AN 37-degree fitting and its SAE counterpart, the JIC 37-degree fitting. Functionally, they appear to be interchangeable, but they are not the same from a standards standpoint. Will JIC 37-degree fittings work for automotive use? Sure, but they are not as strong and you will find limited styles/sizes in JIC. Don't be tempted by the lower price point when plumbing your ride. Stick with true AN-style fittings from respected aftermarket fitting companies and you'll be fine.

1. The typical AN size is referred to as a dash number, as in -6 (and stated as “dash six”). The dash number is equal to the outside diameter of hard tubing in 1⁄16-inch increments. Therefore, a -6 would be equal to 3⁄8-inch tube OD (6x1⁄16=6⁄16=3⁄8). Inside diameter can vary due to wall thickness, but it is generally accepted that tube OD and hose ID are the same for AN hose selection requirements (see sidebar chart at end of story).

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2. Just to offer some comparison images, we have here from left to right a -20 hose used for radiator inlet/outlet, a -6 hose used for a fuel line, and a -6 PTFE hose used for power steering fluid—all with a US quarter for comparison.

3. Comparing the two -6 hoses side by side you can see the thinner wall of the PTFE hose makes for a smaller overall hose and also offers up less weight. PTFE line can be used for fuel systems and is a great way to make those long fuel-tank-to-engine runs easier and save weight.
4. As noted in our opening text, once an AN hose is assembled, you’ll most likely need an adapter fitting for your engine/fuel pump/carburetor/etc. While AN to NPT adapters are quite common, many parts require what is referred to as an ORB fitting. ORB stands for O-Ring Base and this is a special fitting that seals on the O-ring, not the threads or a flare seat. These are common for EFI fuel pumps, regulators, and some carburetors.
5. Specialty adapters abound in the aftermarket and you can usually find the adapter you need by searching the specific part of the industry you’re working in (brakes, steering, and so on). This fitting, from www.hydratechbraking.com, is used to convert standard power rack-and-pinion steering inlet/outlet ports to AN -6 for use with PTFE braided hoses to the power steering pump, assist unit, and reservoir.
6. If you’re planning an EFI conversion or a late-model engine swap, you’ll want to know about the spring-lock-to-AN adapters (like the one shown here from Aeromotive) that allow quick and easy fuel line assembly to the modern quick-connect fuel rails. No longer do you have to have a fuel rail modified with a weld-on AN fitting.
7. As noted in our sidebar at the end of this story, the most popular AN sizes can be assembled/tightened with standard SAE wrenches. You do, however, stand a great chance of marring the aluminum fittings and scratching the anodizing off. In a pinch, some painters tape on the wrench will help, but if you find yourself doing a lot of AN hose assembly, it is best to treat yourself to an actual set of AN wrenches like these. You’ll also find AN adjustable wrenches too.
8. When you’re routing AN braided hose, be sure to protect all painted surfaces. It’s something first time users don’t think of until they pull a length of AN hose through a panel and find out they’ve worn the paint right off their fender. The braided steel covering is like a saw.
9. Planning your routing is paramount to a successful installation, too. Just like the braided hose covering can damage your paint, we’ve seen loose braided hose cut through wiring harnesses and other rubber hoses. Use rubber coated clamps, called P-clamps by many, to secure your braided hose run and prevent abrasion.
10. This under car photo of our Generation Gap project shows what we mean about securing your braided hose runs. Use rubber grommets for any panel pass through and rubber coated clamps every 8 to 12 inches.

To properly plumb your vehicle with AN hose, you have to determine the proper hose size and material first. You'll find several different hose materials available, so read the manufacturer's literature and/or speak with the company's tech line to ensure you are going to use the right hose material for your application. Once you've determined the hose requirements, you need to determine the proper end fittings for the hose. Generally, the more gradual the turn the better fluid flow you will achieve, though in the real world sometimes a 90-degree fitting is your only option. Just keep in mind it is better to have a 45-degree or straight fitting and let the bend occur in the hose if at all possible. You can also find 120-, 150-, and 180-degree fittings from most manufacturers and sometimes these are used due to space constraints or simply for build aesthetics. With your hose material and end fittings determined, the last piece of the puzzle is any necessary adapter fittings. While you can buy some automotive performance parts pre-configured for AN hose fittings, most likely you'll be in need of some AN to NPT (pipe thread) adapters for your intake manifold, transmission cooler lines, and so forth. Once you have everything, it's time to build your hose assembly.

Assembling AN hose is a fairly straight forward operation and while there are special hose cutters, assembly tools, and even AN-specific wrenches available to make the job easier, you truly can create AN hose assemblies with traditional handtools you already have. Let's start with cutting the hose to the proper length for the job. Mark the hose location for cutting and then wrap the marked area with a few tight loops of electrical tape. To cut the hose, you can use a 32-tooth hacksaw, electric or pneumatic cut-off wheel, or hose sheers. The hacksaw works well for larger AN hose, while we generally use a cut-off wheel for our project's smaller hose work. Once the hose is cut, remove the tape from the hose end. A nice solid cut will keep the wire braided cover compact and tight to the hose. If the wire braid has flared outwards it can be tough to insert into the AN fitting's socket. If you only have one or two wire strands sticking out, you can carefully snip them with cutters.

A bench-top vise with a pair of "soft jaw" inserts is real handy for this next step, but we've done it with our bare hands as well. Push the hose end into the AN fitting's socket with a counterclockwise twist until the hose end stops against the bottom lip of the socket. Finally, lubricate the AN fitting's nipple and insert it into the socket and hose assembly by hand. Thread the fitting as far as you can by hand and then finish with the proper sized wrench. You want 1⁄16-inch or less gap between the fitting's hex and socket. Wrap up the hose build by flushing the hose with solvent and blowing out any trash with compressed air. These steps are for standard rubber-based braided hose for use with AN fittings. Assembling Teflon lines, often used for high-temperature and/or high pressure applications like transmission oil coolers, power steering lines, and so forth, takes a few extra steps. Undoubtedly, the easiest AN hose type to assemble is the "push-on" or "push-lock" hose. As its name implies, you simply lubricate the fitting and push it into the end of the hose section. This style of hose has its limitations, but is very popular for aftermarket EFI conversion kits. Check out our captions below for more details on each type of hose and how to assemble them properly.

Push-On Hose

We'll start with the easiest hose to assemble, which is the push-on or push-lock style of hose. This hose is offered in several materials/colors and some even use a nylon-woven outer jacket for protection over just the bare hose. You can also add your own nylon hose sleeving during assembly to complement or contrast your engine compartment. Push-on hose is often rated for 300 psi, which is well above the requirements for such things as oil coolers, fuel lines (even EFI), and such, but is not suitable for high-pressure applications such as power steering or brake lines. Push-on hose does not require any special tools and is easy to assemble on the workbench or even directly on the vehicle.

11. This sample of push-on hose is from a FAST EZ-EFI system and as you can see, it is labeled for fuel injection use with a 150 psi rating. The SAE J-number is also imprinted on it as well.
12. AN push-on fittings use a special hose barb nipple, seen here just lightly pressed into the hose. One you’ve determined your hose length and have cut the hose end square (a hose cutting tool makes the job easy), the AN fitting’s nipple is lubricated and pressed into the hose end until the hose seats against the hose insulator (the gold ring crimped on the fitting shown).
13. The finished assembly will look as such. Push-on hose fittings will usually rotate in the end of the hose to allow better hose routing/alignment (you don’t want any twist in your hose from fitting end to fitting end with the fittings installed and tight), however, the only way you’ll remove the fitting is by cutting the hose end open.