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.
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.
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.
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.
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.
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.
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.
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 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.
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.