JIC 37° Flare Fittings

The 37° flare connection makes its seal metal to metal, between the coned nose of the fitting and a matching 37° seat. On a tube assembly the tube itself is flared to 37° and pulled against that nose by a sleeve and nut; adapter to adapter, two opposing seats simply draw up against one another. No O-ring, no sealant, no tape.

It is the oldest connection still in everyday hydraulic use, and it has lasted because the parts are inexpensive, the sealing area is small enough to seal at modest assembly torque, and a damaged flare can be re-cut on site with hand tools. SAE J514 and ISO 8434-2 fix the dimensions, so a body from one supplier mates with a tube nut from another.

Where it's specified

• General hydraulic plumbing — tube runs on agricultural, construction and industrial machinery built around inch dash sizes.
• Field repair — flares can be formed and re-formed in the workshop without seal kits or special tooling.
• Standards conversion — JIC adapters are the usual bridge between inch tube and ORB, NPT, BSP or metric ports.
• Low-torque assembly — the narrow seat seals without the clamp load a face-seal or flange joint demands.

Range and materials. Straights and unions, male and female swivels, 45° and 90° elbows, run and branch tees, crosses, bulkhead fittings, caps, plugs, tube nuts and sleeves, and conversion adapters, in dash sizes -02 through -32. Carbon steel with trivalent zinc plating, stainless steel and brass are all listed; material-specific ranges are broken out in the steel and stainless sections.

Ordering notes. Dash size refers to tube outside diameter in sixteenths of an inch, not to the thread — a -08 fitting takes 1/2 in tube on a 3/4-16 thread. Seats are machined rather than lapped, so a scored or out-of-round flare should be re-cut instead of tightened harder. Brass and stainless carry lower pressure ratings than steel in the same size.