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JIC Fittings Vs. AN Fittings: What's the Difference?

A brief look at the design and history of 37 degree flare fittings.

37° flare fittings are a very robust system that has proven itself in various industries over the nine decades, or so, that they've been in service. They use a cone-tipped male thread that mates either to a female coned seat or the inner taper of a flared tubing end. When you mate JIC threads with tubing, you use a pressure-distributing sleeve and nut to apply pressure to the tubing flare and maintain the seal.

Assembly diagram for 37 degree fittings. The nut on the left engages first with the pressure sleeve, then with the tubing flare, and finally secured to the male stud to lock all components in place.

This is a metal-on-metal seal that's perfect for high temperature and/or pressure and holds up well to vibration. Let’s take a deeper look into JIC and what makes them such a successful connection type.

History and Design

The idea of a 37° flare fitting began long before JIC was established as a standard under SAE J514. Originally, these fittings were designed to a very tight tolerance for use by the US Army and Navy during WWII. Labeled as AN (Army Navy fittings), these were very high-performing fittings that gained a solid reputation in both automotive and aerospace applications.

Such a great reputation, in fact, after the war many companies attempted to produce their own flare-style fittings with varying levels of success. Without a clear standard to adhere to, many fittings were not compatible with one another.

In 1950 the Joint Industry Council (JIC) determined that they would develop a standard that manufacturers could use to produce this type of fittings. With the help of a committee of engineers from the Society for Automotive Engineers (SAE) they did just that. They kept much of what had made AN fittings great, but standardized on a lower class of threads (JIC - 2A/2B vs AN - 3A/3B) tolerance so that manufacturers could produce them easier and more affordably.

Who Uses JIC Fittings?

Originally, 37-degree fittings were used for fuel and oil systems (including use as hydraulic fittings for fluid power application). Today, they're still used for these applications, but they've also been adopted by many other industries including water treatment, carwash, and chemical transfer systems.

Should JIC Be Used With AN Fittings?

As mentioned above, AN is produced to an extremely tight tolerance standard. JIC was standardized at a more attainable tolerance level to keep manufacturing costs and difficulty down. This means that a system that uses the AN standard may suffer if tolerances are too loose. Not to mention that the system may not be able to meet any pressure rating guarantees if the wrong type of fitting is used.

Where Could 37° Fittings Be Used?

37° fittings are very versatile when it comes to their range of use. Three things to consider to decide if JIC is the right choice are pressure rating, fitting material, and media density.

1.      Pressure Rating – pressure ratings differ with fitting material, manufacturer, or temperature. Be aware of your specific fitting manufacturer‘s guidelines and follow them for pressure and temperature usage.

2.      Fitting Material - JIC fittings are available in many different materials including brass, steel, stainless steel, aluminum, and titanium. Some fitting materials may be more or less compatible with other fittings or the media flowing in your system. So be sure and identify compatibility before deciding on a material.

3.      Media Density – Since JIC uses a metal-on-metal seal, it is not ideal for lighter gasses. Media of this type may be able to seep through the microscopic imperfections on the metallic surfaces. In this case, a fitting type that uses a rubber or other soft material may be desirable.

37 Degree Tube Flaring

To use JIC fittings with rigid tubing, the end of the tubing must be flared to 37° to match the coned seating surface of the male fitting. This is why JICs are often referred to as 37-degree flare fittings. To accomplish this, use a flaring tool specifically designed for this type of flare. It is imperative to remember to place the nut and sleeve on the tubing before you flare it as they will not be able to slip over the tube once it is flared.

Manual or hydraulic flaring tools are both available. Though, while the hydraulic unit may be easier to operate, it also comes with a hefty price tag.

Flaring can take some skill to get right. For this reason, some have transitioned to a flareless fitting system like Superlok i-Fitting.

When to Replace a Flare Connector

JIC and AN connectors can start to show wear after a while, especially if the connection is disassembled and reassembled often. A few things to look for are scarring on the cone seat, collapsing on the male cone, or loosening the crimp that holds the female threads onto the female swivel connectors.

This image shwos a heavily worn JIC male stud.
Worn male 37°
  1. Scarring – small scratches and wear on either cone seat can prevent a good seal. This may arise due to frequent re-installations or installing the connection with foreign debris on the sealing surfaces.
  2. Cone Collapse – If a flare connection is over-tightened, you may start to see the tip of the male cone start to collapse inward. This can lead to a restriction of flow, weakened seal potential, or an outright leak.
  3. Loosened Swivel Crimp – This is also the result of over-tightening. As the two parts are forced well beyond proper installation torque, the male cone can begin to push the female cone through the crimped-on swiveling threads. Just like cone collapse, this can cause weakened seal potential or leaks.

The Author

Ethan McNeese
Marketing Specialist
Ethan is our resident content marketer, blog author, YouTube host, and general knower of things. When he's not at his keyboard working on new web pages and videos, he's usually out in the shop wrenching on valve assemblies, developing diagrams for projects, or praying for rain.

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