Popular Hydraulic Fitting Types and How to Identify Them

Popular hydraulic fitting types are best sorted by the way they seal. The common groups are O-ring fittings, mated-angle flare fittings, and tapered-thread fittings. That matters because the thread may only pull the connection together; the actual seal may be an O-ring, a flare seat, a flange face, or pipe-thread interference.

For HGW buyers, identify the sealing family first. Then confirm thread, size, gender, body shape, material, pressure rating, temperature range, media, and whether the installed fitting is adjustable, non-adjustable, straight, elbow, tee, plug, or adapter.

Use STAMP as the first sorting step

A practical way to begin is STAMP: Size, Temperature, Application, Media, and Pressure. Size confirms the connection and flow path. Temperature checks both ambient and fluid conditions, including the seal material where an O-ring is part of the connection. Application tells you whether the fitting is on mobile equipment, industrial machinery, a pump, a valve, a cylinder, or a protected manifold. Media covers hydraulic oil, fuel, gas, water, chemicals, and corrosion exposure. Pressure confirms whether the fitting family and part rating fit the system.

STAMP does not replace thread identification, but it prevents the common mistake of matching a fitting visually while ignoring the operating environment. A fitting that looks correct can still be wrong if the seal material, pressure range, or application temperature is not suitable.

O-ring fitting types

ORB fittings

SAE O-ring boss fittings use straight threads and an O-ring near the base of the male thread. The O-ring seals against the machined female port. Adjustable ORB elbows and tees use a locknut and washer so the body can be oriented before final tightening. Non-adjustable ORB plugs and straight connectors install directly into the port without needing orientation.

ORFS fittings

O-ring face seal fittings place the O-ring in the face of the fitting. The O-ring compresses against a flat mating face, making ORFS a strong option for hydraulic systems that see vibration, impulse, or leak-sensitive service. When checking an ORFS replacement, inspect the O-ring groove, the flat face, the tube nut or sleeve, and the connection on the opposite end.

O-ring flange fittings

O-ring flange connections are used on larger hydraulic ports where flow and pressure requirements make threaded fittings less practical. The O-ring seals at the flange face while bolts or clamps hold the joint together. For larger ports, compare code, bolt pattern, flange thickness, and O-ring groove condition before choosing flange adapters and plugs.

O-ring material and temperature checks

For O-ring fittings, the temperature rating is not only about the metal body. The O-ring compound has its own temperature and media limits. Nitrile is common in many hydraulic connections, while fluorocarbon or other compounds may be needed for higher temperature, chemical exposure, or special service conditions. If the old fitting failed near the seal, record the fluid, operating temperature, cleaning chemicals, and whether the O-ring was hard, swollen, cut, or flattened.

Mated angle fittings

Mated-angle fittings seal where two angled metal surfaces contact each other. 37 degree JIC fittings are common in U.S. hydraulic equipment, including hose assemblies, agricultural machinery, construction equipment, and other mobile hydraulic systems. JIC fittings use straight threads to pull the connection together, but the seal is made at the 37 degree flare seat.

SAE 45 degree flare fittings can look similar to JIC fittings, but they use a different seat angle and should not be substituted for JIC connections. They are more often associated with lower or medium pressure service such as automotive, refrigeration, fuel, gas, vacuum, and plumbing-style applications. With any flare fitting, inspect the male nose and female seat for scoring, cracks, distortion, or contamination before reusing a connection.

Tapered thread fittings

Tapered pipe threads seal by thread interference, often with the correct sealant practice. NPT pipe fittings are common in the United States and Canada, but NPT should not be treated as interchangeable with BSPT or metric thread forms. A pipe thread may start by hand even when the thread angle, pitch, or sealing method is wrong.

BSP fittings use British Standard Pipe thread forms; BSPT is tapered, while BSPP is parallel and usually seals differently. Metric hydraulic fittings can also look close to pipe-thread parts, so buyers should record thread diameter, pitch, seat style, and equipment origin before choosing a Metric / DIN 2353 fitting or another metric connection. Do not force a tapered pipe thread into a straight-thread O-ring port.

How to identify the fitting family

• Look for an O-ring at the thread base, on the face, or in a flange groove.
• Check whether the sealing surface is a flare seat, flat face, pipe thread, washer, or O-ring port.
• Measure thread diameter and pitch after the sealing method is known.
• Compare the fitting body shape and orientation, especially for adjustable elbows and tees.
• Record temperature, media, pressure, and material when an O-ring or soft seal is part of the connection.
• Do not assume two fittings are interchangeable because the thread starts by hand.