Plumber’s Union — How To Build Braided Hoses With AN Fittings

In the world of high-performance engines, there is nothing more ubiquitous than the image of stainless-steel braided lines, outfitted with the iconic red and blue AN fittings, carrying vital fluids and gasses to their respective components. While the imagery might be iconic, the components don’t exist for sheer aesthetics. The robust lines and fittings are just as functional as they are good-looking.

The one downside, if you can call it that, to these lines and fittings is the additional steps needed to properly assemble them as opposed to just slipping a rubber hose over a nipple on a component and tightening a worm clamp. Of course, the additional security and strength of the connections — no to mention the aesthetics, if we’re being honest — far outweigh the effort required to properly plumb your system.

While push-lock style AN fittings and hoses do exist, they don’t offer the pressure rating of the traditional AN fittings and braided hose. Since they are a totally different style of fitting and hose, and their assembly is much different, we won’t be looking at those, today.

Measuring your hoses can be a little tricky, since you need to account for the bit of hose that sits inside of the fitting. Also note the tightly wrapped electrical tape before marking the cut. This helps prevent the cut ends from fraying.

Hose In Different Area Codes

There are a number of different braided hoses on the market today. First and foremost, as we covered in this article, regardless of what type of hose you want to use, you will want to stick to quality manufacturers. The discount/knockoff brands might look nice on paper (or in the Amazon/eBay listing) but at the end of the day, a failure can cost far more than just the price of the replacement hose.

The two main types of hose we’ll be covering (since they both use the same tools and procedures in assembly) are the stainless braided and nylon braided types, so let’s look at them. The first, and most familiar, is the stainless-steel braided line. This line is typically composed of a rubber core, which can vary in composition based on manufacturer, from basic rubber in low-end hose to high-tech synthetic elastomers in higher-end hose. That core will be flexible and all-fluid-safe, so compatible with gasoline, diesel, ethanol, and methanol, as well as oil, water, and chemical coolants. There is also a PTFE-core variant, but since it requires different hose ends, it’s outside the scope of this article.

Cutting AN Hose

When cutting braided hose, there are a lot of different methods that have popped up in an effort to get a clean cut. We prefer a good set of dedicated hose-cutting shears with good, sharp blades and long handles for lots of leverage. The trick is to make a smooth cutting motion for a clean cut.

That core then has a sleeve made of tightly woven stainless wire braided around it, in order to provide additional strength as well as abrasion resistance. For the nylon-braided hose, the core is the same, but nylon thread is woven around the core instead of stainless steel. This offers reduced weight and increased flexibility over stainless-braided hose, at the cost of some burst strength, and some abrasion resistance. It still offers a high-enough pressure rating and secure enough hose end attachment to handle all standard plumbing tasks in your car.

AN Fittings Explained

AN fittings get their name from a World War II US military specification (before the term “mil-spec was a thing) that standardized the design and sizing of the fittings between the Army and Navy — hence the “AN” designation. The mating ends are a flare fitting design, using a 37-degree flare angle to form a gasketless, fluid- and gas-tight seal.

AN fittings have a standardized sizing convention, often referred to as “dash size” ranging from -2 (dash two) up to -32 (dash thirty-two). The number after the dash refers to the nominal hard tube outside diameter, or flexible hose inside diameter, in sixteenths of an inch. So a “-8 AN” braided hose would nominally have an inner diameter of 8/16ths — or 1/2 — of an inch.

This cool gauge from Speedway Motors highlights the standardization of AN sizing. If you’re trying to identify any unknown fittings or lines, this inexpensive tool makes short work of that. It sizes hard tubes, braided hoses, and the fittings themselves.

To be clear, the specific fittings we are using on hoses are “AN hose ends.” As mentioned earlier, there are push-lock style AN hose ends, but for braided hose, the fittings use a two-piece compression design, that compresses the hose against the inside of the mating nut, through a mating cone inserted into the ID of the hose.

This makes for a secure connection, capable of withstanding significant pressures (approaching 1,000 psi ratings for most brands of hose and fittings), while also being something that the average person can assemble themselves. By contrast, fittings that need to be crimped on require extremely expensive, complex crimping equipment.

There are a range of hose end designs within each size of fitting. Straight fittings and 90-degree swivel fittings are probably the most common, but there are also a range of obtuse-angled fittings, including 30-, 45-, and 60-degree fittings (since they refer to the angle of deviation from the centerline of the hose, not the included angle. There are also a number of acute-angled fittings (greater than 90 degrees, in this case), including 120-, 135-, 150-, and 180-degree swivel hose ends for unique plumbing challenges.

The key points here are the fittings on the left and right sides. Notice, we used a combination of 90-degree AN fittings and a variety of angled hose ends (30-degree on the right, and a 90-degree on the left) to make the more complex bends. This keeps the hose itself from being forced into any tight bends that could cause kinking.

Tools Of The Trade

When it comes to performance plumbing, the average enthusiast is absolutely capable of plumbing their own project. However, like most projects, to do everything the right way, as efficiently as possible, some specialty tools are necessary. The first specialty tool might not seem like a necessity until you assemble a few hoses without it, and that is Koul Tools AN Hose Assembly tool. All it will take is a couple of times wrestling with slightly frayed braiding, and stabbing your fingers with stainless strands, and you’ll be ready to skip a couple of trips to Starbucks to cover the cost of the Koul Tools.

Here you can see the Koul Tool AN Hose Assembly Tool make short work of what is the most universally disliked part of performance plumbing. The coupling nut is fitted into the clamshell tool (left), and then the tapered throat of the tool is lubricated (center). Finally, the clamshell is placed in a vise, and the hose is inserted with a firm twisting motion. The amount of time and frustration the Koul Tool saves is incredible.

The next tools you’ll need are a bench-mounted vise and a set of aluminum vise jaws. Since the fittings are all aluminum, and the jaws of a standard vise are steel, you can mar the finish of the fittings, without a set of soft jaws. A number of vendors sell aluminum vise jaws made specifically for AN fittings, that have 120-degree notches to securely hold the fittings on four sides instead of just two. Between the soft material and the increased support, the fittings come out unscathed.

A good set of soft jaws not only protects your AN fittings from damage, but as you can see, the design securely holds fittings in a variety of angles to make life easier.

Next, you’ll need some good wrenches. For hose assembly, you’ll want to carefully use your normal steel wrenches on the threaded portion of the AN fitting. However, for connecting fittings to one another, you’ll want to use dedicated AN wrenches.

Like the vise soft jaws, AN wrenches are made of aluminum and designed to not mar the finish of the fitting, while also designed to help prevent overtightening. You’ll also need a good set of cutters to be able to cut the hose. If you want to be fancy, you can use a rotary or oscillating cutter for that purpose as well, and some electrical tape to keep the cut ends from fraying. Finally, you’ll need some form of lubricant and a source of compressed air.

AN fittings assemble by seating the braided hose into the coupling nut (left). Then, the tapered section of the swivel portion of the fitting (right) is lubricated, placed into the I.D. of the hose and the fitting is screwed into the coupling nut. The tapered mandrel traps the hose against the inside of the coupling nut with enough force to withstand over 900 psi of line pressure.


Building The Lines

The best way to learn how to plumb a car is through hands-on experience (nothing to it but to do it), but we’ll walk you through the process. The first step is crucial and isn’t even technically part of the assembly process, and that is measuring the hose. You’ll want to measure at least twice before you cut once and thoughtfully plan out your runs, mitigating any sharp turns by using angled fittings instead of trying to bend the hose in tight radii.

Once you have a general location for your cut, you’ll wrap a two-inch section of hose tightly with electrical tape (ideally, an inch on either side of the cut line) and measure/mark your cut point, remembering to account for the bit of hose that sits inside of the fitting itself. Then using your cutters, you want to make a quick clean cut through the hose. If by chance you have some stragglers, clean up the edges with side cutters before removing the tape from the end of the hose you plan to assemble.

If you have a set of Koul Tools, you simply place the fitting’s nut in the tool, lubricate the tool’s forcing cone, hold it in the vise and push the hose into the nut while twisting. The Koul Tool funnels it perfectly into the fitting and Bob’s your uncle. If you don’t have the Koul Tool, you will need to carefully twist the nut onto the end of the hose without perforating your fingertips.

Once the cone is inserted and the threads started, you will need to use a steel wrench to tighten down the assembly.

Once the hose is seated inside the nut, you lubricate the inside of the hose and the cone of the swivel fitting, secure the hose and nut in the vise jaws, and then insert the cone into the hose opening until you can start the threads. You will then tighten the fitting, making sure you aren’t pushing the hose out of the locking nut, until the fitting bottoms out, or the resistance is heavy.

At that point, you should have a secure connection capable of holding 900- pounds per square inch of pressure. To be sure, give the hose and fitting a tug. If you are able to move the fitting at all, it’s not properly assembled and you need to start over. Once you have repeated the process on the other side, and are happy with your line, you need to make sure that you blow out the line with compressed air, thoroughly. Any debris left in the line after assembly will likely be post-filter on whatever system you are working on and will be free to wreak havoc on your engine, whether it is the fuel system, oil system, or cooling system.

When you are connecting male and female AN fittings, you want to use specific AN wrenches. They are not only sized for AN fittings, but are made of aluminum to prevent marring of the finish, and are shorter to help prevent overtightening of the fittings.

Installing Your New Lines

Once built, it’s simply a matter of connecting the hose ends to their respective AN fittings, and you’re all set. But, there are still a few things to remember. First, is that the fittings are aluminum, which is softer than steel. So if you are using standard wrenches on your AN fittings, take extra care not to damage them. Also, the 37-degree flare mating surfaces do not use gaskets, so there is no “squish” when tightening them, if you overtighten a fitting, you can crack a flare, causing leakage.

Another thing to be aware of, is if you do find a slow leak in one of your joints, tightening the fittings might not be the answer. If, by chance, you have a fitting that isn’t sealing well, Koul Tools has a product called the “Fitting Fixer”. It is a lapping tool that will put a perfect 37-degree mating surface on a male AN and can repair worn or damaged fittings, allowing them to seal like new again.

While plumbing your car with braided lines and AN fittings might seem intimidating at first, with the right tools and a little elbow grease, you are absolutely able to do the job yourself. Not only will you have incredibly strong, secure fluid lines on your project, but lines that look great as well. Plus, the pride of knowing you did it yourself.

These aren't a "must-have" but they sure are nice for any kind of storage situation. These plastic plugs and caps are sized for AN fittings and will seal your lines from any potential contaminants during transport and storage of your engine and lines. This whole assortment was under $20.

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About the author

Greg Acosta

Greg has spent nineteen years and counting in automotive publishing, with most of his work having a very technical focus. Always interested in how things work, he enjoys sharing his passion for automotive technology with the reader.
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