Popular Hydraulic Fitting Types and How to Identify Them
HGW Hydraulics on Jan 27th 2021
Popular hydraulic fitting types are best sorted by the way they seal. The key groups are O-ring fittings, mated-angle 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, 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, Material, and Pressure. Size confirms the connection and flow path. Temperature checks both ambient and fluid conditions. Application tells you whether the fitting is on mobile equipment, industrial machinery, a pump, a valve, a cylinder, or a protected manifold. Material covers steel, stainless steel, brass, plating, 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.
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.
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.
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.
Mated angle fittings
Mated-angle fittings seal where two angled metal surfaces contact each other. JIC 37 degree flare fittings are common in U.S. hydraulic equipment. SAE 45 degree flare fittings look similar to some buyers but use a different seat angle. They should not be substituted for JIC connections.
With flare fittings, threads pull the joint tight, but the threads are not the seal. Inspect the male nose and female seat for scoring, cracks, distortion, or contamination before reusing a connection.
Tapered thread fittings
Tapered pipe threads such as NPT seal by thread interference, often with the correct sealant practice. They are widely used, but they should be handled carefully because repeated assembly can damage the threads. NPT is not the same as BSPT, and tapered pipe thread should not be forced 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, 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.
- Do not assume two fittings are interchangeable because the thread starts by hand.
Related HGW categories
FAQ
What is the easiest way to identify a hydraulic fitting type?
Start with the sealing method. Check whether it seals by O-ring, flare, face seal, flange face, compression bite, or tapered pipe thread.
Are JIC and SAE 45 degree flare fittings interchangeable?
No. They use different seat angles. A fitting may thread together and still fail to seal if the angle is wrong.
Why do O-ring fittings leak?
Common causes include damaged O-rings, dirty grooves, scratched mating faces, wrong material, poor orientation, over-tightening, or using the wrong fitting family.