Every hydraulic fitting is a decision about where the seal is made. The options are few and physical: a 37° cone pressed metal to metal, a flat face squeezing an O-ring, an O-ring crushed into a machined boss, tapered threads wedging on their flanks, a ring biting into tube wall, or a gasket clamped between flanges. Threads supply clamping load; the sealing surface holds pressure.
The section is arranged around those six mechanisms rather than by shape, because the mechanism cannot be substituted. Each family answers to its own document — SAE J514 for 37° flare, J1453 for O-ring face seal, J1926 and ISO 11926 for boss ports, ASME B1.20.1 for NPT, ISO 8434-1 and DIN 2353 for flareless metric, ISO 228 for BSPP, SAE J518 for split flanges. Mixing two at one joint leaks however hard it is torqued.
Where it's specified
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Hydraulic Adapters — the thread-to-thread core: JIC 37° flare, ORFS, SAE ORB, NPT, NPSM swivels and flareless bite type
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BSP and Metric & DIN Fittings — British and European port standards, where a 60° cone, bonded seal or DIN 2353 ferrule replaces the SAE seat
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SAE Flanges and Weld Fittings — pump, motor and cylinder ports past the limit of threaded sizes, plus permanent shop-made joints
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Quick Disconnects, Brass, Caps & Plugs — lines broken routinely, low-pressure and instrument work, and ports closed for shipping
Range and materials. Straights, 45° and 90° elbows, tees, crosses, bulkheads, swivels, reducers and cross-standard adapters, in zinc-plated carbon steel, 316/316L stainless and brass, with metric and BSP sizes alongside the dash range.
Ordering notes. Work outward from the end you cannot change, the port on the pump, valve or cylinder. Never identify a thread by eye: measure OD and check pitch, since 37° JIC and 45° flare, and NPT and BSPT, will start into each other and then fail. On a straight-thread port the O-ring seals; sealant only contaminates the fluid.
