JIC Fittings Guide › JIC vs SAE 45° Flare
JIC 37° vs SAE 45° Flare Fittings
JIC 37° and SAE 45° flare fittings look almost identical, and at several dash sizes they even share the same thread. They are not interchangeable: the seat angles differ by 8°, so a mixed joint touches on a narrow edge rather than a full cone and is prone to leaking. This guide explains the differences, which sizes are easy to confuse, and when each type is used. Background on JIC sizes is in the main JIC fittings guide.
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Standards and Typical Uses
JIC 37° flare is defined by SAE J514 and ISO 8434-2 and is the standard flare connection for hydraulic tube and hose. SAE 45° flare is defined by SAE J512 (automotive tube fittings) and is typically used with soft copper, aluminum or thin steel tube in refrigeration, HVAC, fuel, gas and lower-pressure automotive or plumbing lines. Brass is the most common 45° material.
Thread Comparison by Dash Size
| Dash | Tube OD | JIC 37° thread | SAE 45° thread | Threads mate? |
|---|---|---|---|---|
| -4 | 1/4" | 7/16-20 | 7/16-20 | Yes — seats differ |
| -5 | 5/16" | 1/2-20 | 1/2-20 | Yes — seats differ |
| -6 | 3/8" | 9/16-18 | 5/8-18 | No |
| -8 | 1/2" | 3/4-16 | 3/4-16 | Yes — seats differ |
| -10 | 5/8" | 7/8-14 | 7/8-14 | Yes — seats differ |
| -12 | 3/4" | 1-1/16-12 | 1-1/16-14 | No (pitch differs) |
Thread sizes per SAE J514 and SAE J512 for common sizes; confirm against your supplier's catalog. Because -4, -5, -8 and -10 share threads, a 45° nut can spin onto a 37° male. That is exactly why mismatches get installed.
How to Tell Them Apart
- Use a seat angle gauge. This is the only reliable test. Hold the 37° and 45° blades against the cone; the correct one sits flush with no light gap.
- Look at the flare. A 45° flare is visibly flatter and wider than a 37° flare on the same tube size.
- Consider the application. Copper refrigeration and gas lines are almost always 45°; hydraulic steel tube and hose ends are almost always 37°.
- Check markings and material. Brass suggests 45° (though brass JIC exists); plated steel suggests JIC.
Why Mixing Them Leaks
A flare seals by pressing two matched cones together across a band of contact. With 37° against 45°, contact is reduced to a thin ring at one edge. It may hold briefly at low pressure, but it is sensitive to vibration and over-tightening can crush the flare. Use the correct mating part or a proper adapter.
Which Should You Use?
- Hydraulic systems: JIC 37° (or ORFS where leak resistance is critical — see JIC vs ORFS).
- Refrigeration, HVAC, gas and soft copper tube: SAE 45°, following the governing code for that service.
- Motorsport and aerospace: AN, which uses the 37° flare — see JIC vs AN.
FAQ
Are JIC and 45° flare fittings interchangeable?
No. JIC uses a 37° seat and SAE 45° flare uses a 45° seat. Even where threads match, the seats do not seal properly together.
Which sizes of JIC and 45° flare have the same thread?
Common sizes -4 (7/16-20), -5 (1/2-20), -8 (3/4-16) and -10 (7/8-14) share threads. -6 (9/16-18 JIC vs 5/8-18 45°) and -12 (1-1/16-12 vs 1-1/16-14) do not.
How do I check the flare angle?
Use a seat angle gauge with 37° and 45° blades. The matching blade sits flush against the cone.
Where are 45° flare fittings used?
Mostly with soft copper or aluminum tube in refrigeration, HVAC, gas, fuel and lower-pressure automotive lines.
Is a 37° flare the same as AN?
AN fittings use the same 37° flare angle and threads as JIC, with tighter tolerances.
Related guides
- JIC Fittings Guide (main)
- JIC vs NPT
- JIC vs ORFS
- JIC vs AN
- How to Identify a JIC Fitting
- JIC Thread Size Chart
- -4 JIC Fittings
- -6 JIC Fittings
- -8 JIC Fittings
- -10 JIC Fittings
- -12 JIC Fittings
- -16 JIC Fittings
- JIC vs BSPP
- JIC vs Metric (DIN 24°)
- JIC Torque Specs
- JIC Fitting Types
- JIC Materials & Pressure Ratings
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