JIC Fittings Explained: 37 Degree Flare Seals and Common Uses
Aug 3rd 2023
A JIC fitting is a hydraulic fitting that seals at a 37 degree flare. The threads pull the two halves together, but the fluid seal is made by metal-to-metal contact at the flare seat.
This design makes JIC fittings common in hydraulic hose assemblies, mobile equipment, industrial machinery, and many service environments where standardization and availability matter.
What JIC Stands For
JIC stands for Joint Industry Council. In current hydraulic work, JIC usually refers to SAE 37 degree flare fittings governed by SAE-style dimensional standards.
The standard became common because it helped equipment builders and maintenance teams use repeatable hose and tube connections across many machines.
How JIC Sealing Works
A male JIC fitting has a 37 degree cone. A female JIC fitting has a matching 37 degree seat. When the nut is tightened, the cone and seat make metal-to-metal contact.
The threads are straight and do not seal the fluid. If the flare is scratched, distorted, contaminated, or the wrong angle, the connection can leak even when the threads feel tight.
Why the 37 Degree Flare Matters
The 37 degree angle separates JIC from SAE 45 degree flare and other similar-looking connections. A small angle mismatch can leave poor contact at the seal surface.
This is why identification should include the seat angle, not only thread diameter and pitch. Many wrong replacements happen because the fitting looks close on the bench.
Materials and Construction
JIC fittings are available in carbon steel, stainless steel, and other materials. Carbon steel is common in many hydraulic systems. Stainless steel is chosen for corrosion resistance, washdown, chemical exposure, and longer service in demanding environments.
Material choice affects corrosion resistance and durability, but it does not change the sealing principle. The flare and thread size still have to match.
Compatibility With AN and JIS
JIC and AN fittings both use a 37 degree flare, but they come from different specification histories and should be compared by actual dimensions, material requirements, and pressure expectations before substitution.
JIC and JIS can look similar but are not the same. JIS often uses different thread forms and flare details. Forcing one into the other can damage the seat or cause leakage.
Sizes and Identification
JIC fittings are commonly described by dash size. To identify one, measure thread diameter, thread pitch, and confirm the 37 degree flare seat.
Use a pitch gauge and calipers rather than guessing from wrench size. The wrench flats do not define the connection standard.
Applications, Advantages, and Limits
JIC fittings are used on hydraulic hose assemblies, agricultural equipment, construction machines, hydraulic power units, industrial presses, and serviceable fluid lines. They are popular because they are widely available and do not require an elastomer at the flare seal.
The limitations are also clear. Metal-to-metal flare seals can be damaged by over-tightening, vibration, scratches, or repeated assembly. In severe leak-sensitive service, ORFS or other O-ring sealing styles may be preferred.