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.

Stainless Braid Rubber Hose

Moving on to the more traditional stainless braid style of AN hose you'll see there are a few more steps involved in making a complete hose assembly. The stainless braid itself makes the hose assembly a bit trickier, but the stainless braid look is what most people want, plus the braid is what protects the hose and gives the hose its strength. Traditional stainless braid is the most common, but we're seeing some hose companies offer a dark gray or black stainless covering now as well if you're looking for something a bit on the modern or OE side for a late-model engine swap for example. You'll find the broadest applications for fuel, oil, and more in the stainless braid hose, as well as the largest offerings in dash sizes too.

14. Once you’ve determined the length of your AN hose routing, the end must be given a clean cut (or the excess hose cut from the run length). As mentioned in our opening text, a high-speed cut-off wheel does a great job, though many use AN hose shears or even a sharp chisel and hammer.
15. Push the freshly cut hose end into the AN hose fitting socket with a counterclockwise turning motion until the hose end seats against the stop inside the socket as seen here. Getting all of the wire braid inserted is often the hardest part (and where everyone pokes their fingers). Stray wire strands can often be clipped with cutters if you only have one or two strands giving you trouble.
16. Lubricate the hose nipple and threads on the AN fitting using assembly lube or a light oil. This will help start the nipple into the opening of the rubber hose and prevent galling the threads on aluminum fittings
17. Use a piece of tape at the base of the AN socket to act as an indicator and then thread the AN fitting into the socket. Soft jaws in a vice can be used to secure the socket or you can simply use the age-old “two wrench method” of threading the fittings together. The tape applied at the base of the socket is used to verify the hose did not push out of the socket as the AN fitting was threaded in. If the tape line has moved, you’ll need to disassemble the AN fitting and try again. You want the fitting and socket to be within a 1⁄16-inch or closer.

PTFE Lined AN Hose

For high pressure applications (or if you're looking to save weight for some compatible fluid line runs), a PTFE (Teflon) hose with stainless braid is the answer. This hose is a little different in its assembly and we feel it can be the trickiest of the three AN hose types discussed here. The PTFE hose requires a special three-piece fitting (standard AN hose fittings are just two). The three piece fitting is used to give the PTFE hose the support it needs to seal at the fitting. The thin, flexible tubing otherwise would not seal (similar to a compression fitting for the plastic or copper tubing used on the water line for your refrigerator).

18. PTFE AN hose requires special three-piece fittings. The fitting is made up of a socket, olive, and nipple, shown here from left to right.
19. As with standard rubber-based stainless braid AN hose, you will have to determine your hose length and then mark, tape, and cut the hose accordingly. Once you’ve cut your PTFE hose to length, and before you remove the extra tape from the cut end, slip the socket end of the fitting over the stainless braid, ensuring the threaded end faces the cut end of the hose.
20. To install the olive, you have to remove the remaining tape that secured the stainless braid during cutting, carefully spread the braid open and away from the PTFE hose, and then press the olive over the end of the PTFE hose until it is seated squarely into the olive. Pushing the hose itself into the olive, supported against a block of wood is a good option.
21. The PTFE hose requires seating into the ribs found inside the olive. While some manufacturers state the nipple portion of the AN fitting can be used for this step, we prefer to use a tapered punch gently pushed into the PTFE hose to do the job.
22. Once the PTFE hose is seated to the olive, the nipple of the AN fitting can be lubricated and inserted into the hose until the olive seats against the base of the fitting, as seen here. Lubricate the threads of the AN fitting and thread the socket onto the fitting by hand. Finally, tighten with the proper wrench until you have 1⁄16-inch or less gap between the fitting and the socket

AN Fitting Specifications

While the complete range of AN fittings is from -2 to -32, the most commonly used sizes for automotive use are -3 to -24. Generally you will find -3 used for brake hoses, -4 used for nitrous system lines; and -6, -8, and -10 are most commonly found in fuel systems. The larger AN sizes are often only found in cooling system hoses and can be quite expensive by the foot, not to mention the cost of having the radiator, water pump and heater inlet/outlet converted to AN thread via adapters or welding new fittings in place.

AN Size Tube OD/Hose ID Thread Size Pipe Thread Size Std. Wrench Size
-3 3⁄16-inch 3⁄8-24 SAE 1⁄8-27 NPT N/A
-4 ¼-inch 7⁄16-20 SAE ¼-18 NPT 9⁄16-inch
-6 3⁄8-inch 9⁄16-18 SAE 3⁄8-18 NPT 11⁄16-inch
-8 ½-inch ¾-16 SAE ½-14 NPT 7⁄8-inch
-10 5⁄8-inch 7⁄8-14 SAE N/A 1-inch
-12 ¾-inch 11⁄16-12 SAE ¾-14 1¼-inch
-16 1-inch 15⁄16-12 SAE N/A 1½-inch
-20 1¼-inch 15⁄8-12 SAE N/A N/A
-24 1½-inch 17⁄8-12 SAE N/A N/A

Stop Poking Your Fingers

One of the most aggravating parts of AN hose assembly is trying to insert the freshly cut end of a stainless braid hose into the AN fitting's socket. More often than not blood is drawn as the hose slips around on the inlet of the socket and the individual stainless wires poke your fingertips. It's not a pleasant feeling; one that we can attest to having endured dozens of times over the years making AN hoses for various project cars. Now you can put the box of Band-Aids away thanks to the invention of Koul Tools. With the Koul Tool, you simply insert the AN fitting's socket into the tool, place the tool into your vice, and push the AN hose into the end of the tool. The tool's funnel like action helps direct the hose's stainless braid into the socket with ease, and best of all, not a drop of blood or a single curse word will ensue! Koul Tools are available for all popular sizes of AN hoses used in automotive projects and the company's latest tool, the EZ-ON hose press, is designed to help assemble push-on style hose without any fuss, too. You can find Koul Tools at Summit Racing, along with AN wrenches and all manner of AN hose and fittings.

Tricks and Tips of AN Hose Assembly

Now that you've gone through our complete guide on assembling AN hoses and fittings, you're probably itching to head out to the garage and try building a hose for yourself. Well, hold on a minute there sparky; we've got a few more tips to make sure everything goes smoothly for you and your hose building adventures.

You get what you pay for with AN hardware. Stick with known products and don't buy farm-quality stuff at the flea market.

Stick to one brand. Not all brands are the same, and while they all transfer fluids well, fitting sizes, fitting-to-hose compatibility, and even colors (one company's black is not the same as another company's black) can differ. Find a company with the fittings you need in the color you want and stick with them for your project.

Keep your fluid flow routing as gentle as possible. A twisting, turning path of 90- and 180-degree fittings is going to cause restriction and generate heat in your fluid transfer. Use as many straight fittings as you can and gentle hose bends.

Use you vice (you do have a vice in your shop right?) with a set of soft jaw vice inserts (pictured here) to protect and secure your fittings during assembly.

AN fittings are reusable, but PTFE hose fittings should be reassembled with a new olive.

AN sealing washers are available to help seal fittings to adapters when quality or brand differences cause minor leaks.

AN hose with stainless braid can cause surface damage if not secured, including cutting through wiring and hoses. Always use clamps and high-strength tie wraps to secure your hose runs or cover the braid with anti-chafe covering.

When choosing the proper AN hose you need to determine pressure, temperature range, and fluid compatibility— carbureted line pressure is much different than EFI line pressure, for example. If in doubt, ask the manufacturer.

Hose assembly routing/design should always take into consideration that the hose must not be kinked, twisted, or have an excessive bend radius once installed.

Lubricate all end fitting and adapter threads before installation; do not thread dry aluminum parts together.

Attach one end of the hose and just snug the end fitting, this allows the opposite end to be threaded and the hose to rotate for the best routing and to prevent twisting. Tighten both ends only after the hose is properly oriented.

Flush all hose assemblies after installing end fittings and blow out with compressed air. If the line is for a high-pressure application, we suggest having the assembled hose pressure tested at your nearest hose crimping/hydraulic outlet.