Measuring 37 Degree JIC Fittings for Replacement
HGW Hydraulics on Sep 7th 2021
JIC fittings are widely used in hydraulic systems because they use straight threads and a 37 degree flare seating surface. The threads draw the connection together, but the seal is made at the flare. That is why measuring a JIC fitting requires more than checking thread diameter.
A correct replacement should confirm thread size, thread pitch, male or female style, and the 37 degree flare seat.
Thread size
Start by measuring the thread. For a male JIC end, measure the outside diameter of the threaded section. For a female JIC end, measure the inside diameter of the threaded opening. Use calipers when possible, and measure the cleanest part of the thread rather than a crushed or worn edge.
JIC thread sizes are expressed in inches and are commonly matched to dash sizes. Do not rely on a rough visual estimate. Several hydraulic threads can look close in a photo, and a wrong thread can damage the mating part.
Thread pitch
After measuring diameter, count the number of threads per inch. This is the thread pitch. A thread pitch gauge is the easiest tool because each blade matches a specific pitch.
The correct blade should sit cleanly in the threads without rocking. If the pitch is wrong, the fitting may start by hand but bind before it seats. Forcing it can damage the thread or the sealing surface.
Male and female JIC ends
A male JIC fitting has external threads and a 37 degree flare nose. A female JIC fitting has internal threads and a matching 37 degree flare seat. Some female JIC ends are swivels, so the nut and seat should be inspected together.
Many adapters have JIC on only one side. The other side may be NPT, ORB, ORFS, BSP, metric, hose-end, bulkhead, cap, plug, or another fitting family. Record both sides instead of assuming the whole part is JIC.
Flare angle
The flare angle is the identifying feature. A JIC fitting uses a 37 degree flare. The angle can be verified with a flare gauge or by comparing the seat to a known 37 degree JIC reference.
Do not confuse JIC with other flare styles. A fitting can appear to thread together and still fail to seal if the seat angle is wrong. Also inspect the flare surface for scratches, dents, corrosion, crushed edges, or contamination. A damaged flare can leak even when the thread size is correct.
Final replacement notes
Before ordering, record whether each end is male or female, the measured diameter, thread pitch, flare condition, body shape, material, and installed orientation. A straight 37 degree JIC fitting, elbow, tee, bulkhead, cap, plug, or conversion adapter may share the same JIC end but fit the machine differently.
If the old connection leaked at the flare, inspect both mating pieces. Replacing only one side may not fix a damaged seat on the other side.