JIC vs JIS Fittings: Seats, Threads and Identification
JIS fittings from Japanese machines use a 30° seat and BSPP-type or metric threads. Here is how they differ from JIC 37°, and the sizes that look closest.
Last updated October 30, 2026. Reference values; verify against manufacturer specifications.
JIS fittings come from Japanese machinery, especially excavators, loaders and tractors. They often turn up on equipment that also has JIC hoses. They are not compatible with JIC: the seat angle is different, the threads are different, and on many JIS ends the male and female seats are the reverse of JIC. This page explains each difference and lists the sizes that look closest.
The short answer
- Seat: JIC uses 37°; JIS uses 30°.
- Threads: JIC uses inch UNF/UN threads with a 60° form. JIS parallel fittings use 55° parallel pipe threads to JIS B0202, which are the same as BSPP. JIS-metric (Komatsu-style) fittings use metric threads.
- Interchange: none. Even where a diameter is close, the thread form or pitch is different, so the joint will not seal. Use an adapter.
JIC vs JIS at a glance
| Feature | JIC 37° (SAE J514) | JIS 30° (Japanese Industrial Standard) |
|---|---|---|
| Seat angle | 37° from centreline | 30° |
| Male end | Convex 37° cone nose | Concave 30° seat (inverted, per Eaton) |
| Female end | Swivel nut with 37° seat | Swivel nut with 30° cone |
| Thread form | 60° UNF / UN, inch | 55° parallel thread to JIS B0202 (same as BSPP), or metric on JIS-metric/Komatsu-style ends |
| Size naming | Dash size = tube OD in 1/16 in | Nominal pipe size (1/4, 3/8, 1/2...) or metric thread |
| Typical equipment | North American industrial and mobile machines | Japanese construction and agricultural machines |
The inverted seat
On a JIC fitting, the male end carries the cone: a convex 37° nose in front of the threads. The female swivel nut has the matching seat inside. Eaton's identification guide describes the JIS 30° flare differently. The male has an inverted (concave) 30° seat, and the female has the 30° cone. If a male fitting has a recessed, funnel-shaped seat instead of a nose, it is not JIC and may well be JIS.
The Alfagomma technical guide makes a related point. British BSPP fittings with a 60° cone and Japanese 30° fittings use similar threads but are still not interchangeable, because the seats are different.
JIS thread sizes vs JIC
JIS parallel threads use the same sizes and pitches as BSPP (G) threads, and Eaton describes them as interchangeable with BSPP threads. The table compares each size with the nearest JIC thread. JIS fittings are sold by nominal size, so a "1/2 JIS" thread actually measures about 21 mm (0.83 in) across.
| JIS / BSPP size | Thread major diameter | TPI | Closest JIC | JIC OD / TPI | Diameter difference |
|---|---|---|---|---|---|
| G1/4 | 13.16 mm (0.518 in) | 19 | -5 (1/2-20) | 12.70 mm / 20 | 0.46 mm |
| G3/8 | 16.66 mm (0.656 in) | 19 | -6 (9/16-18) | 14.29 mm / 18 | 2.37 mm |
| G1/2 | 20.96 mm (0.825 in) | 14 | -10 (7/8-14) | 22.23 mm / 14 | 1.27 mm |
| G3/4 | 26.44 mm (1.041 in) | 14 | -12 (1-1/16-12) | 26.99 mm / 12 | 0.55 mm |
| G1 | 33.25 mm (1.309 in) | 11 | -16 (1-5/16-12) | 33.34 mm / 12 | 0.09 mm |
| G1-1/4 | 41.91 mm (1.650 in) | 11 | -20 (1-5/8-12) | 41.28 mm / 12 | 0.63 mm |
| G1-1/2 | 47.80 mm (1.882 in) | 11 | -24 (1-7/8-12) | 47.63 mm / 12 | 0.18 mm |
| G2 | 59.61 mm (2.347 in) | 11 | -32 (2-1/2-12) | 63.50 mm / 12 | 3.89 mm |
JIS/BSPP diameters per ISO 228-1 as listed in the Eaton and McGill guides; JIC per SAE J514. Diameter difference is calculated.
Three pairs need care:
- JIS 1 (G1, 11 TPI) vs -16 JIC (1-5/16-12): the diameters are within about 0.1 mm. Only the pitch (11 vs 12 TPI) and the thread form tell them apart.
- JIS 1-1/2 (G1-1/2, 11 TPI) vs -24 JIC (1-7/8-12): the diameters are within about 0.2 mm. Again, check the pitch.
- JIS 1/4 (G1/4, 19 TPI) vs -5 JIC (1/2-20): the diameters are within about 0.5 mm and the pitches are close.
A 55° Whitworth thread gauge sits flush on a JIS/BSP thread, and a 60° inch gauge rocks. Over 1 in of thread length, an 11 TPI thread and a 12 TPI thread differ by one full thread, so count carefully over a whole inch.
JIS-metric (Komatsu-style) fittings
Some Japanese machines use 30° fittings with metric threads instead of BSPP-type threads. These are often called Komatsu-style or JIS-metric. Published guides do not agree on which metric thread goes with which dash number. Eaton and McGill pair several sizes differently. To avoid that confusion, measure the thread and use the thread itself as the size. The metric threads below are listed by both guides:
| Metric thread | Major diameter (mm) | Pitch (mm) | Major diameter (in) |
|---|---|---|---|
| M18x1.5 | 18 | 1.5 | 0.709 |
| M22x1.5 | 22 | 1.5 | 0.866 |
| M30x1.5 | 30 | 1.5 | 1.181 |
| M33x1.5 | 33 | 1.5 | 1.299 |
These metric threads also turn up on European DIN 24° fittings. So measure the seat angle too: 30° points to JIS-metric, and 24° points to DIN. More on metric look-alikes is on the JIC metric conversion chart.
How to tell a JIS fitting from a JIC fitting
- Look at the male end. A convex cone nose suggests JIC (37°) or DIN (24°). A recessed, concave seat suggests JIS 30°.
- Gauge the thread. Try an inch 60° gauge, a Whitworth 55° gauge and a metric gauge. Only one should sit flush along the full length.
- Measure the diameter. Compare it with the table above, or enter it in the finder on the JIC identification page.
- Measure the seat angle. A seat gauge that sits flush at 30° confirms JIS. At 37°, the fitting is JIC or AN.
Connecting JIS equipment to JIC hoses
The usual fix is an adapter with a male JIS (or JIS-metric) end on one side and a male JIC end on the other. Order the JIS side by thread and seat type, not only by the nominal size, since sellers use different naming. If the port on the machine is a BSPP port rather than a 30° flare connection, see JIC vs BSP for the port-side options.
References
Eaton Thread Identification Guide (JIS 30° flare, JIS B0202 threads and JIS-metric sizes); McGill Hose thread identification guide (Japanese and Komatsu-style sizes); Alfagomma technical pocket guide (British vs Japanese seats); ISO 228-1 thread dimensions; SAE J514 JIC dimensions as published by Parker and Eaton. Values are reference only.
Frequently asked questions
Is JIS the same as JIC?
No. JIS fittings use a 30° seat and BSPP-type or metric threads, while JIC uses a 37° seat and inch UNF/UN threads. They do not interchange.
What thread does a JIS fitting use?
JIS 30° flare fittings with parallel threads use JIS B0202 threads, which share the sizes and pitches of BSPP (G) threads. JIS-metric or Komatsu-style fittings use metric threads such as M18x1.5 or M22x1.5.
Can I connect a JIS fitting to a JIC hose?
Not directly. Use an adapter with the correct JIS end on one side and a JIC 37° end on the other.
Are JIS and BSPP threads interchangeable?
Eaton's guide describes JIS B0202 parallel threads as interchangeable with BSPP. The seats on JIS 30° flare fittings and BSPP 60° cone fittings are different, though, so the joints are not interchangeable.
How can I tell JIS from JIC by eye?
Check the male end. JIC has a convex 37° cone nose. Many JIS male ends have a concave 30° seat instead. Then confirm with a thread gauge and seat gauge.