JIC 37 degree flare (SAE J514)
The general hydraulic 37 degree flare. Metal to metal on the cone, no seal of any kind.
60 degree flanksParallel37 degree flare cone
Confusion pair
JIC 37 vs SAE 45 degree flare
The single most common mis-identification in the trade. Six of the eight shared sizes have exactly the same thread and a different cone angle, so they screw together and the joint weeps.
SAE 45 degree flare (SAE J512)
The 45 degree flare found on refrigeration, fuel, brake and gas lines. Often brass. Not a high pressure hydraulic connection.
60 degree flanksParallel45 degree flare cone
The three answers
What actually happens if you put them together
What interchanges
- Nothing. The two are never interchangeable, at any size, because a 37 degree cone and a 45 degree cone touch on a line rather than on a face.
What threads together and will still leak or fail
This is a safety statement, so it is only made where it is sourced. Each item below either cites a published statement that the two are not interchangeable, or rests on the figures on the size pages showing an identical thread with a different seat.
- At -02, -03, -04, -05, -08 and -10 the threads are identical: 5/16-24, 3/8-24, 7/16-20, 1/2-20, 3/4-16 and 7/8-14 respectively. One identification guide states this outright and warns that the sealing surface angles are not the same; another warns that thread binding occurs when different thread configurations are mixed and says not to do it. The joint will pull up, hold on the bench and weep in service, and tightening harder cold-flows the softer of the two cones instead of sealing it.
- The failure is worse in the direction people usually make it. An SAE 45 flare is a low and medium pressure connection - fuel, brake, refrigeration - so a 45 degree part fitted into a hydraulic circuit is being asked to hold a pressure its body was never rated for, on top of sealing on the wrong angle.
What will not fit at all
- At -06 the two differ outright: SAE 45 is 5/8-18 and JIC is 9/16-18. They will not start on each other, which is the one size where the mistake catches itself.
- At -12 the diameter is the same 1 1/16 in but the pitch is not: SAE 45 is 14 threads per inch and JIC is 12. It will not thread more than a turn.
The check that settles it
Put a seat gauge in the cone, or hold the two side by side. A 45 degree cone is visibly blunter and shorter than a 37 degree cone. Alone it is very hard to judge; against a gauge it takes a second. If you have no gauge, count the threads at 3/4 in diameter: 1 1/16-12 is JIC and 1 1/16-14 is SAE 45.
Size by size
Where the threads match, and where they do not
6 of the 13 sizes below run the same thread count within half a millimetre on diameter. Those are the rows that will screw together. Built from the published dimensions at page-build time, not from a hand-kept list.
| Size | JIC 37 degree flare | SAE 45 degree flare | Will they assemble? |
|---|---|---|---|
| -02 | 5/16-24 UNF · 7.94 mm | 5/16-24 UNF · 7.94 mm | Yes, and it is the wrong joint |
| -03 | 3/8-24 UNF · 9.53 mm | 3/8-24 UNF · 9.53 mm | Yes, and it is the wrong joint |
| -04 | 7/16-20 UNF · 11.11 mm | 7/16-20 UNF · 11.11 mm | Yes, and it is the wrong joint |
| -05 | 1/2-20 UNF · 12.7 mm | 1/2-20 UNF · 12.7 mm | Yes, and it is the wrong joint |
| -06 | 9/16-18 UNF · 14.29 mm | 5/8-18 UNF · 15.88 mm | No - 1.59 mm apart on diameter |
| -08 | 3/4-16 UNF · 19.05 mm | 3/4-16 UNF · 19.05 mm | Yes, and it is the wrong joint |
| -10 | 7/8-14 UNF · 22.23 mm | 7/8-14 UNF · 22.23 mm | Yes, and it is the wrong joint |
| -12 | 1 1/16-12 UN · 26.99 mm | 1 1/16-14 UNF · 26.99 mm | No - 12 TPI against 14 TPI |
| -14 | 1 3/16-12 UN · 30.16 mm | No such size | Only one family has this size |
| -16 | 1 5/16-12 UN · 33.34 mm | No such size | Only one family has this size |
| -20 | 1 5/8-12 UN · 41.27 mm | No such size | Only one family has this size |
| -24 | 1 7/8-12 UN · 47.62 mm | No such size | Only one family has this size |
| -32 | 2 1/2-12 UN · 63.5 mm | No such size | Only one family has this size |
Diameters shown are the basic major diameter of the male thread. On a tapered thread that figure is defined at the gauge plane, which is not where a caliper naturally sits - the size pages carry the span published charts actually measure.
Detail
Everything each family carries
| Property | JIC 37 degree flare | SAE 45 degree flare |
|---|---|---|
| Flank angle | 60 degrees | 60 degrees |
| Parallel or tapered | Parallel | Parallel |
| Seat | 37 degree flare cone | 45 degree flare cone |
| Where it seals | Metal to metal, cone against the flared tube or the mating cone. No O-ring, no sealant. | Metal to metal, cone against the flared tube. No O-ring, no sealant. |
| Defined by | SAE J514, ISO 8434-2 | SAE J512, SAE J533 |
| Sized by | Sized by dash number, which is the tube outside diameter in sixteenths of an inch: -08 is 8/16 in, half-inch tube. | Sized by tube outside diameter in inches rather than by dash number. |
Answers
Common questions
Will a JIC 37 degree flare screw into a SAE 45 degree flare?
At -02, -03, -04, -05, -08 and -10 the threads are identical: 5/16-24, 3/8-24, 7/16-20, 1/2-20, 3/4-16 and 7/8-14 respectively. One identification guide states this outright and warns that the sealing surface angles are not the same; another warns that thread binding occurs when different thread configurations are mixed and says not to do it. The joint will pull up, hold on the bench and weep in service, and tightening harder cold-flows the softer of the two cones instead of sealing it.
Are JIC 37 and SAE 45 interchangeable?
Nothing. The two are never interchangeable, at any size, because a 37 degree cone and a 45 degree cone touch on a line rather than on a face.
How do I tell them apart?
Put a seat gauge in the cone, or hold the two side by side. A 45 degree cone is visibly blunter and shorter than a 37 degree cone. Alone it is very hard to judge; against a gauge it takes a second. If you have no gauge, count the threads at 3/4 in diameter: 1 1/16-12 is JIC and 1 1/16-14 is SAE 45.
More pairs
Other fittings people mix up
Where these figures come from
Every value on this page was checked against 4 independent published sources:
- Hydraulic coupling identification chart E2/50101 - Gates, Gates Europe, 2004 (manufacturer, read 2026-08-27)
- Fluid Ports and Connectors Identification Guide - McGill Hose & Coupling, SAE J512, J514, J1453, J1926-1, ISO 228, ISO 7, DIN 2353, JIS (distributor, read 2026-08-27)
- Master catalogue: conformance, working pressure and torque tables - Tompkins Industries, SAE J514, SAE J1453, SAE J1926-1, SAE J1926-3, ISO 11926-1 (manufacturer, read 2026-08-27)
- SAE threads reference tables - RYCO Hydraulics, SAE J512 (manufacturer, read 2026-08-27)