Steel JIC 37° Flare Fittings

A 37° flare joint seals where the cone on the fitting nose meets the flared face of the tube. Nothing elastomeric sits in the leak path, so the joint is only as good as the finish and form of those two machined surfaces once the nut draws them together. Carbon steel takes a clean, consistent cone off the machine and is hard enough to hold it.

That hardness is why most shops default to steel here. A brass seat cold-flows slightly on each make-up, so a line broken and remade over its service life drifts toward a weep, while a steel seat returns to shape far more often. Steel also carries the highest pressure rating of the three materials in a given dash size and costs the least, which is why the SAE J514 and ISO 8434-2 range is stocked deepest in it.

Where it's specified

• Lines that come apart for service — the seat survives repeated remakes without picking up or flowing out of shape
• Pressure concentrated in small sizes — a -04 or -06 steel body carries more than the same body in brass
• Cost-driven machine builds — the cheapest material, held in depth across the whole dash range
• Sheltered, oily environments — nothing is attacking the zinc plating there

Range and materials. Straights, 45° and 90° elbows, tees, crosses, unions, bulkheads, swivel nuts, caps and plugs from dash -02 to -32, converting at the far end to ORB, NPT, ORFS or BSP. Bodies are free-cutting carbon steel, finished in trivalent (Cr3+) zinc.

Ordering notes. Set flare nuts by flats from finger tight rather than by feel, and keep sealant off the thread — the thread carries load, the cone seals. Inspect the cone first; a scored seat will not be rescued by more torque. The plating is the only corrosion barrier, so any part cut, welded or badly scratched will rust from that point; washdown and marine service belongs in the stainless range.