Screwed on Right: The Pros and Cons of JIC Hydraulic Fittings

By Charles Kolstad, Marketing Manager, Tameson

JIC fittings, also known as SAE J514 hydraulic fittings, are essential components in a wide range of applications. They are extensively used in industries such as agriculture, construction, heavy machinery, and automotive.

Originating from AN fittings developed by Parker and further enhanced by the U.S. military during World War II, JIC fittings quickly gained popularity. The fittings were developed by the U.S. Army and Navy (hence the “AN” in the name) for aviation applications. Subsequently, they were further developed to meet high-performance standards and tolerances.

This article delves into the origins, uses, pros, and cons of JIC fittings, comparing them to AN fittings.

The Beginning: AN Fittings

After World War II, numerous AN flared-fitting designs and specifications flooded the market, causing confusion about which standard to follow. To address this issue, manufacturers needed a specific standard.

The Joint Industry Conference (JIC) standardized the AN design, creating a 2A/2B thread class to simplify manufacturing. This fitting became known as the JIC fitting. It offered high performance at a lower cost and a simpler manufacturing process compared to the AN fitting with a 3A/3B thread class.

The conference aimed for the JIC fitting standard to have the same reputation as the Society for Automotive Engineers International. SAE International represents over 100,000 engineers and experts in the aerospace, automotive, and commercial vehicle industries.

A committee of SAE engineers accepted the task of developing the JIC fitting standard, and their efforts were instrumental in its creation. In 1950, the SAE standard 37° flare fitting was included in SAE J514. In 1986, it became an ISO standard known as ISO 8434, later replaced by ISO 8434-2 in 1996.

Most JIC hydraulic fittings find application in agriculture, construction, mining, and the automotive industry. While not meeting the high-performance standards of AN fittings, the SAE 37° 2A/2B UN/UNF series threads are designed to provide optimum thread fit, balancing manufacturing capabilities, convenience, economy, and fastener performance.

JIC vs. AN Fittings

JIC and AN fittings have similarities in design, function, and size, but notable differences set them apart. One significant difference is economics. AN fittings are considerably more expensive due to their tight design tolerances. They are generally not used unless specifically required by the application.

Threads

AN 37° flare fittings feature male and female fittings produced to class 3A/3B UNJ/UNJF with a radiused root thread. The J screw threads have a root radius that improves the fastener’s tensile stress area and reduces stress concentration in the thread. This makes the thread stronger, providing better fatigue life. AN fittings are commonly employed in military, aerospace, and aircraft applications.

On the other hand, SAE 37° flare fittings (JIC fittings) feature male and female threads made according to class 2A/2B UN/UNF. These classes provide optimum thread fit, considering manufacturing capabilities, convenience, economy, and fastener performance.

Military vs. Industrial Standards

AN flare fittings conform to MIL-F-5509 specifications and the SAE aerospace (AS) standard AS4841. Fittings manufactured under SAE/ISO 37° conform to U.S. Department of Defense MIL-F-18866 and SAE J514/ISO 8434-2 standards.

Materials

AN fittings are commonly made from costly metals or composites, given their applications. In contrast, SAE 37° flare fittings or JIC fittings do not have such requirements and are often made from standard materials. AN fittings are available in carbon steel, stainless steel (CRES), aluminum, titanium, and copper-nickel. SAE 37° fittings are commonly made from carbon steel, stainless steel, and brass.

JIC 37° Flare Fittings Design

AN 37° flare and industrial 37° flare fittings function, operate, and look identical, leading to their interchangeable use. The male JIC fitting connects to a 37° female flare fitting or flared tube, creating a metal-to-metal seal between the flared tube or nose of the female fitting and the male fitting. The compact design is achieved due to the relatively small seal area. JIC fittings offer low-assembly torque, high-temperature, and high-pressure capabilities.

Thread Classes

JIC fittings, according to SAE J514, are designed and fabricated using the 2A/2B thread fit. Thread fit refers to the allowances and tolerances between male and female threads, or how they fit into each other. It measures the tightness or looseness between the threads. There are six standard classes for unified inch threads:

• 1A / 2A / 3A: The thread fit class standard for external or male threads.
• 1B / 2B / 3B: The thread fit class standard for internal or female threads.

All six classes are clearance fits, allowing the male and female fittings to assemble without interference. As the class number increases, the tolerances between the threads become tighter.

• Classes 1A and 1B have highly loose tolerances, making assembly and disassembly quick and easy. These classes are rarely specified outside of low-carbon threaded rod and machine screws.
• Classes 2A and 2B strike a balance between fastener performance, production efficiency, and economy. These thread fits are used in almost all commercial and industrial fasteners.
• Classes 3A and 3B should be used when tight tolerances are required. Safety is crucial in the design of these fasteners. Fittings in these classes have very tight tolerances and no allowances.

UN or UNJ Threads

In North America, the Unified Thread Standard specifies thread forms, series, allowances, tolerances, and designations for screw threads. It standardizes bolts, nuts, and other threaded fasteners. Unified screw threads have a flank angle of 30° and are symmetrical, commonly referred to as 60° threads.

UNC, UNF, and UNEF threads are almost identical to UNJ, UNJC, UNJF, and UNJEF threads. The letter J indicates that these screw threads have a greater root radius (UNJ, UNJC, UNJF, and UNJEF). The larger root radius improves the tensile stress area of the fastener and reduces the stress concentration factor in the thread, resulting in a stronger thread. UNJ threads have standard tolerances of 3A/3B. Bolts with a UNJ thread root have a shallower thread root, making them incompatible with a UN nut, which necessitates the use of a UNJ nut.

Pros and Cons of JIC Fittings

Flared fittings, including JIC fittings, outperform pipe fittings in design and performance. Flared fittings have long replaced pipe fittings in most hydraulic design applications. The advantages of using flared JIC or J514 fittings include a wide selection of fittings in accordance with SAE J514, availability in various sizes and shapes, and interchangeability among different manufacturers adhering to the same standard. Additionally, they are suitable for high-temperature applications since they lack an O-ring.

However, there are some disadvantages to using JIC fittings. For specific applications, such as those with high vibrations, the pressure rating may be lower than required. JIC fittings have a metal-on-metal seal construction, making them suitable only for hydraulic, liquid, and noncritical applications. Assembly of 37° flare fittings can cause nose collapse, which worsens with over-tightening and reduces the flow diameter.

Installing JIC Fittings

JIC fittings should be installed using the flats-from-wrench-resistance method. This simple method ensures that the connection is sufficiently torqued without damaging the fit or thread. The flats method eliminates the influence of plating, lubrication, and surface finishes on torque requirements.

Follow these steps to tighten JIC hose fittings properly:

• Connect the female and male connectors tightly with a wrench until you feel slight resistance. This resistance indicates the wrench resistance point.
• Mark this position on both the male and female fittings using a permanent marker.
• Refer to a JIC fittings chart and rotate the nut further according to the number of flats. Each flat is equivalent to 1/6 of a turn on a hexagonal tube nut.
• Once the nut is tightened to the required number of flats, mark the connections again. This serves as a secondary reference point to check the tightness of the connection over time and as a reminder for reconnection after maintenance.

Acquiring knowledge about which fittings to use in different applications ensures smooth operation and can help save costs.

Keywords: fluid power, hydraulics, JIC fittings