Best AN Plumbing and Hose Practices With Fragola Performance Systems

Plumbing can be frustrating. Just the mere mention of the word can give some people the shivers. There’s nothing like pressuring your handiwork only to watch the leaks pour from every fitting, inevitably raising the blood pressure of even the most even-keeled plumber. Even watching plumbers can be a disturbing experience in most cases.

Fragola Performance Systems


Branching out from the family owned and operated FK Rod End business, Frank Fragola establishes FPS in 2002 as a private label manufacturer in Southington, Connecticut.

Fragola began branding their own line of fittings to support racers in all series of racing in 2005.

Today FK Rod End is the largest manufacturer of spherical bearings in the United States and Fragola Performance Systems employes over 100 people as a genuine American manufacturer of their own parts.


Fortunately for those of us in the automotive industry, plumbing the fluid systems on your car is much more dignified than household plumbing. The level of expertise in automotive plumbing is higher caliber too.

Not that we are making fun of the local pipe-fitters union, but automotive plumbing has roots deep in the aviation industry. The lessons learned in high tech aircraft have migrated into fluid systems of cars, ensuring a high level of precision and skill.

AN Standards

You often hear the terms AN standard and AN Specifications tossed around when discussing fittings and hose ends, but many self-professed auto plumbing gurus don’t understand the specifications or where they came from.

AN Spec is a US military-derived set of specifications that dates back to the pre-World War II era and stems from a joint standard agreed upon by the Army (Army Air Corps) and the Navy Aeronautical communities for military aviation applications. The Army Air Corps adopted flare fitting technology in the 1930’s, eventually developing a 37 degree flare angle fitting with precision threads. These fittings became the standard for military aviation in World War II which eventually led to the commercial aviation industry.

AN fittings have a 37 degree angled surface that acts as the seal and precision threads for longer operational life.

After the war was ended, many versions of the 37 degree flared fittings came into the industrial marketplace with varying differences between the different manufacturer’s products. An organization of joint manufacturers, the Joint Industry Council (JIC) agreed on a set of standards for the AN design with a newer style of thread class for ease in manufacturing. As the new AN fittings began to migrate into other industry, they became known as the JIC fittings.

Seeking SAE standardization for the AN fittings, the Joint Industry Council allowed the SAE to develop new industry standards for the 37 degree flare. In 1950, the SAE J514 fitting was adopted and eventually became an ISO standard (ISO8434) in 1986. In 1996 the previous ISO standard was replaced with ISO 8434-2.

Differences Between AN Flare and 37 degree Industrial Flare 

Initially the primary differences between AN and SAE/ISO 37 degree flared fittings were in the fitting’s threads. AN fittings were made with class 3A/3B UNJ or UNJF threads which are radiused root threads for tighter tolerances and longer fatigue life. SAE and ISO 37 degree flared fittings utilize  2A/2B UN or UNF threads. To add to the already confusing standards, the Military published specifications in MIL-F-5509 for AN flare fittings which were designated Aerospace Standards (AS) with the appropriate AS designated part numbers.

Additional differences between AN and SAE 37 degree flared fittings can be found in material types with the AN fittings including titanium, copper/nickel and stainless steel. SAE 37 degree flared fittings are commonly available in carbon steel, stainless steel and brass. Hex sizes & hex widths can also vary between manufacturers.

AN fittings can be manufactured in many different material types like titanium, copper/nickel and stainless steel, but aluminum fittings are most common in automotive plumbing.

The AN and Industrial 37 degree flare fittings may appear to be the same, and they maybe dimensionally identical but they are not interchangeable. All 37 degree fittings utilize the flared seat “metal on metal” contact for sealing. For the purposes of automotive best plumbing practices, we are focusing strictly on AN fittings, hoses, and their precise tolerances when designing and building your fluid system.

We contacted Jeff Stacy, President of Sales and Marketing for Fragola Performance Systems, to get the top tips and techniques that enthusiasts need to know when plumbing an automobile for performance applications. “The goal is to get a quality, reliable, leak free, high performance fluid system,” said Stacy.

Jeff Stacy, President of Sales and Marketing at Fragola Performance Systems.

What is Automotive Plumbing?

Basically, automotive plumbing is the combination of lines and fittings that contain and allow fluid to move from one component to another. Without these lines there would be no way to get brake fluid to the calipers and no way to get the fuel from the gas tank to the engine.

Engine oil cooling and filtering, transmission fluid, engine coolant, power steering, compressed air, hydraulic clutch systems, nitrous and even mechanical gauges rely on plumbing in order to work.

Basic Components

The goal is to get a quality, reliable, leak free, high performance fluid system. – Jeff Stacy.

The lines that contain compressed air or fluids can either be tubing or hose. Stacy made it clear that Fragola Performance Systems does not manufacture hose but they…”only sell and use quality hose made in America. We sell hoses that are manufactured by Parker Hannifin, a world leader in hose manufacturing, headquartered in Cleveland, Ohio. We also have a partnership with Telefex, a major manufacturer of PTFE-lined hose designed specifically for racing,” he stated.


There’s a wide variety of hose types available for automotive plumbing. Hose is relatively lightweight and flexible which makes it essential for use between components in which there is even the slightest movement. Depending on the

Fragola’s Premium Black Nylon Race Hose

application, choices of single or multiple layered construction are available. Hose construction by the manufacture can be intentionally built for vibration resistance, chemical compatibility, temperature resistance, flexibility, abrasion resistance or corrosion resistance. Careful thought and a little research will go a long way in selecting the best constructed type hose for your application. In addition to AN -3 P.T.F.E. hose assemblies that meet D.O.T. specifications for flexible brake lines with straight, 45 degree angle, banjo or MPT hose ends, Fragola Performance Systems currently offers these types of bulk hoses:

Premium Black Nylon Race Hose

  • Recommended for motorsports applications
  • Black synthetic rubber core that is resistant to oil, fuels, coolants and alcohol
  • 500 psi working pressure
  • Reinforced with a single braid of bright corrosion resistant type 302 stainless steel wire braid
  • Operating temperature range of -40 degrees F to +300 degrees F
  • Designed to be used with FPS series 2000 hose ends and FPS Sport-Crimp hose ends (not intended for use with 3000 series hose ends)

There’s a wide variety of hose, fittings and accessories available on the market. Just because it’s available does not mean you have to use it all. A little planning and a thoughtful system design with quality parts will serve you better in the long run.


Fragola 3000 Series Stainless Race Hose

3000 Series Stainless Race Hose

  • FPS series 3000 race hose is manufactured to aerospace-quality standards for years of trouble-free service
  • 500-1500 psi working pressure
  • 2 layers of woven stainless steel, inner layer resists collapse while the outer layer protects against abrasion
  • Unique inner liner that is compatible with all hydrocarbon and alcohol based fuels along with all synthetic and natural based lubricants
  • Operating temperature range of -40 degrees F to +300 degrees F
  • Designed to be used with FPS series 2000 “Pro-Flow” hose ends,  3000 series race hose ends and FPS Sport-Crimp race hose ends

Fragola’s stainless steel race hose is designed to work with single or double nipple hose-ends and is rated at 500-1500 psi working pressure.


Fragola 6000 Series P.T.F.E. Lined Stainless Hose

6000 Series P.T.F.E. – Lined Stainless Hose

  • P.T.F.E. – lining for corrosive applications like brake fluid. Works well with hot oil and power steering fluid. Handles nitrous oxide with ease.
  • P.T.F.E. powder is extruded into a smooth bore product
  • Stainless steel braided
  • Working pressure based on diameter of hose:
    -3 through -5 has a working pressure of 3,000 psi
    -6 has a working pressure of 2,500 psi
    -8 has a working pressure of 2,000 psi
    -10 has a working pressure of 1,500 psi.

8000 Series Push-Lok General Purpose Hose

  • Manufactured to the same standard as series 3000 race hose but is a perfect alternative when cost or weight savings is a main consideration
  • 250 psi maximum working pressure
  • Synthetic inner layer covered with fiber braid reinforcement and wrapped with a weather resistant textile cover
  • Temperature range to 300 degrees F
  • Designed to be used with series 8000 Push-lite hose ends

Series 8600-8700 Push-Lok Hose

Series 8600-8700 Parker Push-Lok General Purpose Hose

  • The standard for a many applications. Works well when used within the temperature and pressure parameters
  • 250 psi maximum working pressure
  • Operating temperature range of -40 degrees F to +212 degrees F
  • Synthetic rubber tube covered with one layer of textile braid combined with an outer layer of synthetic colored rubber

Also available from FPS are custom factory crimped P.T.F.E. hose assemblies that are easy to order in five basic steps:

  1. Choose hose size and style
  2. Choose hose end for both ends
  3. Choose length
  4. Choose clocking angle of hose ends (when using 45 degree or 90 degree on both ends)
  5. FAX a sketch to Fragola showing the position of both ends

Single nipple hose-ends come in just about any angle or finish that you would ever want. They are simple to assemble and are reusable.


Fittings refers to hose-ends, adapters, unions and reducers used in the plumbing system. Typically made of steel or aluminum, fittings are generally the parts that are used to join the hose or tubing to enter components.

Hose-ends – join the lines to the components. These are the parts that are crimped or screwed or pressed onto the ends of hose or tubing so the hose assembly can be joined to the component. Hose-ends basically come in two different styles, crimped and push on. Crimped hose-ends are commonly used in making complete hose assemblies. Because the crimping dies match precisely, a properly crimped hose-end ensures a precise, leak-free and tear-proof hose assembly. The drawback to crimped hose-ends are in the angle setting when elbow hose-ends are used. Once they are installed, the crimped hose ends do not allow for any angle adjustment.

Press on hose-ends have become more common in automotive applications. They are broken into two main styles, single nipple and double nipple. Press on hose-ends are manufactured for easy installation and reuse. Most are manufactured with a tapered nipple for quick and easy alignment and hose installation.

Single nipple hose-ends, like Fragola’s Series 2000 Pro Flow hose-ends, use the socket to draw the hose over the tapered nipple which seals by providing a crush of the hose between the socket and the tapered nipple. Reuse of the hose-end is typical due to the design of the fitting. Available in a wide variety of angles, from straight and 30 degree hose-ends to 180 degree hose-ends, just about any hose routing angle can be achieved.

Fragola’s Series 3000 Race hose ends are “cutter” style hose ends which rely on the socket to draw the hose over the nipple and into the cutter for a tight seal.

Double nipple hose-ends, like Fragola’s Series 3000 Race hose ends, are commonly called “cutter” style hose ends. In this style of hose-end, the socket draws the hose over the nipple and into the cutter. A seal if formed when the cutter embeds itself into the end of the hose. The number of angle choices are as ranging as the single nipple hose-ends.

Adapters and Unions  – Adapters are fittings that are used to connect hose ends to components that do not have common styles. They are used to join hose-ends of different types or sizes, these fittings “adapt” one size or style of fitting to another size or style. Unions on the other hand are a type of adapter that is used to join hose-ends or a hose-end to a component when both parts are the same size and style.

Good plumbing practices can keep you from being broken down on the track or the side of the road.

Best Plumbing Practices 

With so many different plumbing components, available in a wide variety of materials and construction, there are endless chances to make a mistake when you layout and assemble your automotive plumbing system. According to Stacy, the first thing that you need to keep in mind when designing your system is; “Before you make a mistake, call us.”

By now we should be in agreement that going to the hardware store and using any old fitting and piece of hose off the shelf isn’t going to cut it for a quality plumbed fluid system. Sure, there are those that try it, and many times these are the crews that are broken down on the side of the road or sitting dejected in the pits. Plumbing failure is one of the most common contributors to unnecessary failures and breakdowns.

The flip side of the coin is that plumbing success does not need not be difficult or expensive. All it takes is a little knowledge combined with some care and thought. Fragola’s Jeff Stacy has agreed to share with us some of the best plumbing practices that will make a difference in how your plumbed system works for you, not against you.

1. Easy to Install, Inspect and Maintain

“Heavy emphasis on the easy to maintain,” says Stacy adding, “we’ve seen a lot of guys run their fuel lines through the chassis rails. It looks pretty neat but what happens when you get a leak? It becomes a lot more work.” Avoid routing hose through tight areas or long runs through chassis rails. You should be able to inspect and remove each hose section without removing a large number of panels or components.

Almost every hose has a “bending radius,” we’re using a radiator hose as an example here because the kinking in the hose is easier to spot. Bending any hose past it’s bending radius will decrease its ability to transport fluid.

A thoughtful design and layout of plumbing is not only easier to install but the components can be easily inspected, repaired or replaced. Routing hoses in a manner to avoid damage to the hose by stretching, crushing, kinking or abrasion by rubbing against other components is critical to assure maximum performance from your plumbing system. Hose assemblies should be routed in a manner that if a failure does occur, the escaping fluid will not cause personal injury.

Many times a hose manufacturer will publish a “bending radius” for hose. These bending radius numbers refer to the minimum radius that a hose may be bent and still allow maximum working pressure through the hose. Running a hose down the frame rails and bending it with a tight radius at the end of the run to connect with a component can lead to a loss of mechanical strength and eventual hose failure.

Designing your plumbing with the eye of a maintenance man is the key here. If the hose is easy to install, it’s probably going to be easy to inspect, simple to maintain, and easy to replace if there is a problem.

Keeping unused fittings in a clean, cool, dry area away from sunlight will prevent any degradation of the O-rings or coatings.

2. Use Quality Components

“Many times products off the shelf are not up to the specifications that we meet here domestically. That’s why you are seeing some manufacturer’s fittings that leak because of porous material or different manufacturing standards,” Stacey mentioned. Checking to ensure that fittings are certified to AN standards is not only smart but can prevent a plumbing nightmare before one ever exists. It’s tough to disagree with the principle of using components with a solid reputation for quality and strength.

Storing hose and fittings properly will ensure that your quality components stay in functional shape. Hose assemblies should be considered as safety relevant components which need to be cared for and inspected as such.

Keeping hose stored in a clean, cool and dry area will help keep the material in tip-top shape. Avoiding exposure to direct sunlight, moisture or corrosive chemicals will keep the hose in functional condition.

While fittings don’t have the same requirements for direct sunlight, moisture and chemicals can be an issue. Care should be taken to store hose-ends and fittings in clean, dry containers or packages. Fittings with O-rings have a shelf life and should be marked with dates. O-rings can degrade as a result of normal environmental conditions, which can lead to leakage or contamination in the plumbing system. Careful inspection and avoiding long shelf life will eliminate the possibility of installing a fitting that may leak.

This -8 AN fitting is typical use in fuel, oil or transmission lines. Most fittings have published temperatures and pressure limits so that components can be matched to handle the minimum and maximum temperatures.

3. Build Your System to Handle the Work

Good hose and fittings have published temperatures and pressure limits so that components can be matched to handle the minimum and maximum temperatures and maximum pressures for the systems you are designing. “Under no conditions should anyone use an unrated fitting or hose, or ones that are rated below your system’s capability,” says Stacy. “It’s unsafe. Especially in systems carrying hot oil or pressurized fuel,” he added.

Granted, hose manufacturers usually design their hoses with a safety factor to ensure that a hose will not burst within the published operating range. That safety factor can be as much as 4:1 times the published working pressure. Even with that extra measure of safety, selecting hose that is rated for the pressure and temperature of your system’s normal operation is crucial in building a plumbing system that will handle the job.

A key factor in building your plumbing system is compatibility. “The hose, tubing and fittings should all be compatible with the fluid they will be carrying,” said Stacy. “If your plumbing is designed to move methanol fuel from the fuel cell to the engine, the hose needs to be compatible with that fuel. Otherwise the hose’s inner layer may break down causing leaks or sending particles into your fuel injection or carburetor.”

When a hose, fitting O-rings or the fittings themselves breakdown due to incompatibility with the fluid being transferred, high velocity fluid discharge, explosion or burning of the fluid and injuries resulting from inhalation, ingestion or skin exposure can result.

4. Design With the Fewest Joints, Unions and Connections

“The latest trend is building cars lighter. To be competitive or gain a little competitive edge, build your systems as light as safely possible. Going to the hardware store for fittings is going to result in bulky and heavy fittings. Buying our specialized racing fittings and hose-ends will result in a stronger and lighter system,” claims Stacy. In addition to saving some unnecessary weight, designing a system with fewer fittings has another benefit. “Fewer connections means fewer potential leak points,” says Stacy.

Taking advantage of the wide variety in fittings available will help. Stacy gave us this example, “Let’s say you need to route a hose or tube 180 degrees. You can use two 90 degree fittings and it will do the job but choosing a 180 degree fitting will accomplish the same thing with less weight, and more importantly, fewer potential leak points.”

Part of choosing the best fitting is knowing what is available. To get a good idea of the different types of fittings on the market, check out Fragola Performance Systems online catalog by clicking here.

AN Fitting to Inch Size Conversion

Dash Size    Inch Size            Typical Use

-04                    ¼”          Gauge lines, Vacuum lines
-06                    3/8”        Fuel return lines
-08                    ½”          Fuel, Oil, Transmission
-10                    5/8”         Fuel, Oil, P/S pump
-12                    ¾”           Fuel, Oil, P/S pump
-16                    1”              Coolant Lines
-20                   1 ¼”         Coolant Lines


Torque Specs for AN Fittings

Dash Size           Torque

-3                         8¾ ft/lb
-4                         11½ ft/lb
-6                         16¼ ft/lb
-8                         29 ft/lb
-10                       35 ft/lb
-12                       45 ft/lb
-16                       70 ft/lb
-20                       85 ft/lb


5. Don’t Overlook Torque

Tightening the hose-end to the fitting can cause a problem if not done correctly. According to Stacy, “Aluminum has a tendency to gall, so we recommend a drop of oil on the fitting’s threads.”

Galling is a form of surface damage arising between sliding solids, distinguished by roughening and creation of protrusions on the surface.

“A drop of oil can help prevent any galling when fittings from different manufacturers are used. Obviously we’d prefer that a builder only use our fittings, but it’s important to keep in mind that threads between different manufacturers can be slightly different. That difference can cause galling or tightening problems,” said Stacy, adding that torquing the fittings will prevent over-tightening and stretching the fitting’s flared surfaces. “Once the flared surface is marred, scratched or stretched, the possibility of a leak is greater.”

6. Size Matters

We’ve discussed selecting tubing, hose or fittings that are rated for the pressure they will be operating within, and we can easily understand how tubing strength is related to the size of the wall, but we should also consider the size of the fitting. For example, the larger the tube diameter is, the less strength it has. “Maximum recommended operating pressure goes down as the tube or hose size goes up,” says Stacy.

The size of the hose and fitting matters. The size of the components must be adequate to keep pressure drops to a minimum or to prevent the hose from aging due to heat generated by a higher fluid velocity.

In general, pressurized fluid inside the hose assembly varies with pressure and flow rate. The size of the components must be adequate to keep pressure drops to a minimum or to prevent the hose from aging due to heat generated by a higher fluid velocity. In the case of fluid flow, speed equals heat. Lines intended for pressure lines, return lines and suction lines all have different fluid velocity recommendations. The best option is to check with component manufacturers for the recommended hose and fitting size to ensure a trouble free plumbing system.

American Made Products

As a final word, Stacy proudly claimed, “Hose-ends may look alike, but at Fragola Performance we take them seriously. We have spent years researching, testing, and generally perfecting this 50-plus-year-old design. We feel that we make the finest hose-ends ever made. All of our fittings are made from 6061 aluminum to AN specifications. To ensure that you’re getting quality parts made in the USA, look for the FPS stamped into the hex on the fittings.”

Stacy says to “look for the FPS stamped into the hex on the fittings.”

Now that we know what to look for in a professionally plumbed race car, we’re going to be inspecting all of our project cars again. Pipe threads and compression fittings might be fine for household plumbing and toilet installation, but we’ll leave the 45 degree fittings for the pipe fitters.

Armed with the best automotive plumbing practices from Fragola Performance Systems, there’s little chance of being stuck on the side of the road or in the pits because of a leaky fluid system.

About the author

Bobby Kimbrough

Bobby grew up in the heart of Illinois, becoming an avid dirt track race fan which has developed into a life long passion. Taking a break from the Midwest dirt tracks to fight evil doers in the world, he completed a full 21 year career in the Marine Corps.
Read My Articles

Everything Off Road in your inbox.

Build your own custom newsletter with the content you love from Off Road Xtreme, directly to your inbox, absolutely FREE!

Free WordPress Themes

We will safeguard your e-mail and only send content you request.

Off Road Xtreme - The Off Road Magazine

We'll send you the most exciting Off Road articles, news, truck features, and videos every week.

Off Road Xtreme - The Off Road Magazine


We will safeguard your e-mail and only send content you request.

Off Road Xtreme - The Off Road Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

Diesel Army

Hot Rods & Muscle Cars

Engine Tech

Off Road Xtreme - The Off Road Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

  • Diesel Army
  • Hot Rods & Muscle Cars
  • Engine Tech

Off Road Xtreme - The Off Road Magazine

Thank you for your subscription.

Thank you for your subscription.

Off Road Xtreme - The Off Road Magazine

Thank you for your subscription.

Thank you for your subscription.