How to Measure JIC Fittings: Threads, Dash Sizes, and 37 Degree Flare

Measuring a JIC fitting correctly means confirming the end type, thread diameter, thread pitch, dash size, and 37 degree flare seat. A fitting that is close in size can still leak if the flare angle or thread standard is wrong.

JIC threads do not create the seal. The seal is made where the male 37 degree cone meets the female 37 degree flare seat.

What a JIC Fitting Is

JIC fittings are SAE 37 degree flare fittings used in hydraulic and fluid power systems. They are common on mobile equipment, agricultural machinery, construction equipment, hydraulic power units, and industrial lines.

The thread provides clamping force. The angled seat creates the metal-to-metal seal. This is why thread measurement and flare confirmation both matter.

Tools for Measuring JIC

Use calipers for thread diameter, a thread pitch gauge for pitch, and a flare-seat reference or known fitting chart to confirm the 37 degree seat. A ruler can help in a pinch, but it is less reliable for small dash sizes.

If measurements are guessed, the result is often a wrong dash size, a mismatched pitch, or confusion with another flare standard.

Step 1: Identify Male or Female

A male JIC end has external straight threads and a 37 degree cone. A female JIC end has internal threads and a matching 37 degree flare seat.

Do not measure a male cone as if it were a pipe-thread taper. JIC is a flare connection, not a thread-sealing connection.

Step 2: Measure Thread Diameter

Measure the outside diameter of a male thread or the inside diameter reference for a female thread. Use a chart to relate the measured diameter to the nominal JIC dash size.

Because dash size and actual thread diameter are not the same thing, the chart step is important. A -6 JIC fitting does not mean the thread measures six of anything directly.

Step 3: Check Thread Pitch

Use a pitch gauge to confirm threads per inch. Several JIC sizes are close enough visually that pitch mistakes are possible.

If the pitch does not match the chart, stop and recheck whether the fitting is JIC, SAE 45 degree flare, ORB, metric, or another connection family.

Step 4: Identify the Dash Size

Dash size is the common shorthand used for ordering and matching hydraulic fittings. It is tied to tube size, thread size, and fitting family.

Once thread diameter and pitch are known, match them to the JIC size chart. Confirm that the hose, tube, or adapter end on the other side also matches the assembly requirement.

Step 5: Confirm the 37 Degree Flare

The flare angle is the final check. JIC uses 37 degrees. SAE 45 degree flare and some other flare systems can look similar but do not seal correctly against a JIC seat.

A leak after matching the thread size often points to a damaged flare, wrong angle, scratched seat, dirt on the surface, or over-tightening.

Mistakes to Avoid

Do not measure outside diameter only, assume every straight thread is JIC, confuse JIC with ORB, or treat an almost-fit as acceptable. ORB uses an O-ring boss seal, NPT uses tapered threads, and BSPP uses a different thread form and seal method.

For a replacement, record male or female end, thread diameter, pitch, dash size, flare angle, material, and the mating component. Those details prevent repeat ordering errors.