JIC Fittings: 37 Degree Flare Connections Explained
Mar 2nd 2023
JIC fittings are widely used in hydraulic and fluid conveyance systems because they provide a serviceable 37 degree flare connection. They are commonly associated with SAE J514 and are familiar in hose, tube, adapter, and mobile equipment work.
The important detail is that a JIC fitting does not seal by thread interference. The threads pull the fitting together, while the 37 degree metal flare surfaces create the seal.
How JIC Fittings Seal
A JIC connection uses a male flare seat and a matching female flare seat. When the nut is tightened, the two angled metal surfaces meet and form the sealing point.
That means thread size alone is not enough for identification. The thread, flare angle, seat condition, and mating part all have to match. A damaged flare face can leak even when the threads engage correctly.
Why Standards Matter
Hydraulic fittings are not governed by one global connection style. Similar-looking fittings may follow different standards based on industry, equipment origin, or region.
AN fittings and JIC fittings are closely related in shape, but AN parts are manufactured to stricter military or aviation-oriented tolerances. JIC is common in hydraulic and industrial applications where broad availability and serviceability matter.
JIS, Komatsu, and SAE Differences
JIS and Komatsu fittings can look close to JIC fittings, but they do not use the same flare geometry. JIS and Komatsu flare-style connections are commonly associated with a 30 degree flare instead of the JIC 37 degree flare, and their thread systems may follow BSP or metric sizing.
SAE 45 degree flare fittings can sometimes thread onto parts that look similar, but the seat angle is different. If a 45 degree flare is used where a 37 degree flare is required, the fitting may tighten without creating the correct seal.
Advantages and Shortcomings
JIC fittings are popular because they are available in many adapter combinations, including unions, pipe adapters, bulkhead fittings, elbows, tees, reducers, swivels, and crosses. Common materials include carbon steel, stainless steel, brass, and specialty alloys.
The limitation is the metal-to-metal flare seal. In very high-pressure or severe sealing applications, an O-ring style connection may be more appropriate because the elastomer seal can compensate for small surface variations. For normal JIC replacement work, confirm the 37 degree flare, thread, material, pressure rating, and mating seat before installation.