Hydraulics & Fluid Power Reference Library · Measure & Identify

How to Identify Hydraulic Fittings & Threads

A step-by-step counter method for identifying JIC, ORFS, O-ring boss, NPTF, BSPP, BSPT, metric 24° cone and Asian 30° flare fittings, using sight, a caliper, a thread pitch gauge and a seat-angle gauge.

Ref HY-0059SAE J514SAE J1453SAE J1926ISO 8434-1ISO 228-1

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Hydraulic connections seal in one of three ways: on the threads (tapered pipe threads), on a metal seat (flare or cone seats), or with an elastomer (O-ring or bonded seal). The thread holds the parts together and the seal is often somewhere else. To identify a fitting you need its sealing method, its thread (diameter and pitch) and its seat angle if it has one. Getting any of these wrong causes leaks or blow-offs.

How to identify

Look for the seal. An O-ring on a flat face means ORFS. An O-ring at the base of a straight male thread means O-ring boss (ORB) or a metric/BSPP port stud. A cone or flare with no O-ring means a metal-seat fitting (JIC, SAE 45°, BSP 60°, JIS 30°, DIN 24°). Threads with no other seal mean a tapered pipe thread.
Check for taper. Tapered threads (NPTF, BSPT) narrow toward the end. Straight threads stay the same diameter.
Measure the thread OD with a caliper. Measure a male across the crests; measure a female across the thread ID and allow for thread depth.
Measure the pitch with an inch (TPI) and a metric pitch gauge. Try both.
Measure the seat angle with a seat-angle gauge. Seat the gauge flat on the cone or flare and match the angle.
Match the result to a thread-identification chart or the manufacturer's ID guide.

Fitting families at a glance

Family	Seal	Seat angle / feature	Thread form	Quick tell
JIC 37° (SAE J514)	Metal-to-metal	37° flare	UN/UNF straight	Common on North American equipment
SAE 45° (SAE J512)	Metal-to-metal	45° flare	UNF straight	Low pressure, fuel and refrigeration; easily confused with JIC
ORFS (SAE J1453)	O-ring on flat face	Flat face, O-ring groove on male	UN straight	Flat face with visible O-ring
ORB (SAE J1926 / J514)	O-ring under a spot face	O-ring at base of male thread	UN/UNF straight	Port fitting with O-ring and often a lock nut
NPTF (Dryseal)	Thread interference	None	60° tapered	Tapered, no O-ring
BSPP (ISO 228-1)	Bonded seal, O-ring or 60° cone	60° cone on hose ends	55° parallel	Pitch close to NPT, but parallel
BSPT (ISO 7-1)	Thread interference	None	55° tapered	Tapered British thread
Metric 24° cone, L and S series (ISO 8434-1)	Bite ring or O-ring cone	24° cone	Metric straight	Heavy (S) and light (L) series share some threads
JIS / Komatsu 30°	Metal-to-metal	30° flare	BSPP or metric	Japanese-built equipment

Key points

JIC and SAE 45° can share the same thread in some sizes. Only the seat angle tells them apart. A mismatched seat will leak or crack.
BSPP vs NPT: at 1/2 and 3/4 the pitch is the same. Use taper and thread angle to tell them apart.
Metric L vs S: the same tube size can come in both series, with different threads and pressure classes. Confirm the series before quoting.
Use a fitting manufacturer's ID guide and gauge set. Small differences matter.

Common mistakes

Identifying by thread size alone and skipping the seat angle.
Sealing a JIC flare with thread tape. The seal is on the flare, and tape fragments contaminate the system.
Mixing hose ends and crimp specs from different manufacturers after identification.

Governing standards: SAE J514; SAE J512; SAE J1453; SAE J1926; ISO 8434-1, -2, -3; ISO 228-1; ISO 7-1; ASME B1.20.3; ISO 6149.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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