JIC vs JIS Fittings: Flare Angle, Thread Type & Equipment Compatibility

The key difference: JIC has a 37-degree flare seat with imperial UNF straight threads. Full breakdown below.

JIC uses a 37-degree flare with UNF straight threads (SAE J514). JIS uses a 30-degree flare with metric threads (JIS B 2351). The 7-degree difference in flare angle means they will not seal properly if mixed, though they may appear to thread together in some sizes.

Key Differences

JIC has a 37-degree flare seat with imperial UNF straight threads.

JIS has a 30-degree flare seat with metric threads.

Both use metal-to-metal flare sealing, but the different cone angles mean the contact area and sealing geometry are incompatible.

JIC follows SAE J514 and uses dash sizing.

JIS follows JIS B 2351 and uses metric sizing.

JIC is the dominant standard in North American hydraulics.

JIS is standard on Komatsu, Hitachi, Kobelco, and most Japanese-built equipment.

When to Choose JIC (SAE J514)

North American hydraulic systems

Equipment built by US or European manufacturers

Applications where JIC is already the installed standard

When parts availability from local suppliers matters.

When to Choose JIS B 2351

Japanese-manufactured excavators, cranes, and hydraulic equipment

Replacement of existing JIS fittings on Komatsu, Hitachi, Kobelco, or Sumitomo machines

When the OEM specifies JIS B 2351.

Practical Notes

JIC and JIS fittings can sometimes thread together because the thread pitches happen to be close in certain sizes. This is dangerous because the 7-degree flare difference means the seal will fail under pressure. Always verify the flare angle with a visual gauge. JIC-to-JIS adapters are available from hydraulic suppliers that stock Japanese equipment parts.

Common Mistake

Threading a JIC male into a JIS female (or vice versa) because the threads engage. The fitting may feel tight but the flare angle mismatch creates a partial seal that leaks under pressure or vibration.