Fitting identification

Hydraulic fitting types and how to identify them

Eight connection families cover almost every hydraulic hose end. Each has its own page with how to recognise it, a size chart, and what it is commonly confused with.

A hydraulic connection is defined by two things: its thread and its sealing surface. The thread holds the joint together. The seal — a cone, a flat face with an O-ring, or the thread itself — stops the oil. Two fittings can share a thread and still not seal against each other.

This is why hydraulic fittings are grouped into families rather than just thread sizes. Learn to recognise the eight families below and most hose ends on a machine can be named in under a minute.

The eight fitting families

JIC 37°Parallel UN thread with a 37° cone on the male nose. The most common hydraulic connection on North American equipment.

ORFSParallel UN thread with a flat face and an O-ring in a groove on the male end. The leak-free standard on modern high-pressure machines.

BSPBritish Standard Pipe thread with a 55° Whitworth form. Parallel (BSPP, G) for hose fittings, tapered (BSPT, R) for pipe joints.

NPTAmerican tapered pipe thread with a 60° form. Seals on the thread itself; NPT needs sealant, NPTF is the dry-seal version.

Metric DINMetric thread with a 24° cone inside the male, in a light (L) and a heavy (S) series sized by tube outside diameter.

JIS / KomatsuTwo Japanese cone-seat connections with a 30° seat: JIS uses BSP parallel threads, Komatsu uses metric fine threads.

O-ring bossParallel UN thread with an O-ring at the base of the male thread. The standard port connection on North American components.

SAE flangeA flanged head clamped to a port with four bolts and sealed by an O-ring. Used on large, high-flow and high-pressure lines.

Identify a fitting in three questions

Is there a thread? If the hose end is a round flanged head held by four bolts, it is an SAE flange.
Is the thread parallel or tapered? Tapered threads are NPT (60° form) or BSPT (55° form) and seal on the thread.
On a parallel thread, where is the seal? A cone on the male nose is JIC 37° or a 30° flare. A flat face with an O-ring is ORFS. A cone inside the male is BSPP 60° or metric DIN 24°. An O-ring at the base of the thread is an O-ring boss port fitting.

Then measure the thread diameter and pitch to find the size. Open the thread identifier →

Fitting types compared

Family	Thread	Seal	Standard
JIC 37°	Parallel UN/UNF, counted in threads per inch	Metal-to-metal on a 37° cone	SAE J514 / ISO 8434-2
ORFS	Parallel UN/UNF, counted in threads per inch	Elastomer O-ring compressed against a flat face	SAE J1453 / ISO 8434-3
BSP	55° Whitworth form, counted in threads per inch	BSPP: 60° cone, bonded washer or O-ring. BSPT: on the tapered thread with sealant	ISO 228-1 (G, parallel), ISO 7-1 (R, tapered)
NPT	Tapered, 60° form, counted in threads per inch	Thread flanks wedge together; NPT requires sealant	ASME B1.20.1 (NPT), SAE J476 / ASME B1.20.3 (NPTF)
Metric DIN	Parallel metric fine, pitch in millimetres	24° cone, with a cutting ring or an O-ring on the female cone	ISO 8434-1 / DIN 2353
JIS / Komatsu	JIS: BSP parallel (G). Komatsu: metric fine, 1.5 mm pitch	Metal-to-metal on a 30° seat	JIS B 8363 (JIS 30° flare); Komatsu factory standard
O-ring boss	Parallel UN/UNF, same sizes as JIC	O-ring compressed into a chamfer at the port mouth	SAE J1926 / ISO 11926
SAE flange	None on the fitting; four bolts through clamp halves	O-ring in a groove in the flange face	SAE J518 / ISO 6162-1 (Code 61) and ISO 6162-2 (Code 62)

What to expect by machine origin

Machine makers tend to follow the standards of their home region. This is a starting point only: fittings vary by model, year and component supplier, and many machines mix several families. Always measure the fitting.

Machine origin	Fitting families commonly found
North America	JIC 37°, ORFS, SAE O-ring boss, NPT, SAE flange
Europe	Metric DIN 24° (light and heavy), BSPP, ORFS, SAE flange
United Kingdom	BSPP and BSPT, with metric DIN and ORFS on newer machines
Japan and Korea	JIS 30° flare, Komatsu 30° flare (Komatsu), ORFS, SAE and metric flanges
China	Metric cone fittings and BSP, with ORFS and SAE flange on newer machines

Frequently asked questions

What are the main types of hydraulic fittings?

JIC 37° flare, O-ring face seal (ORFS), BSP (BSPP and BSPT), NPT, metric DIN 24° cone, JIS and Komatsu 30° flare, SAE O-ring boss, and SAE split flange (Code 61 and Code 62).

How do I identify a hydraulic fitting?

Check whether the thread is parallel or tapered, find the sealing surface (cone, flat face with O-ring, O-ring at the thread base, or the thread itself), then measure the thread outside diameter and pitch and match them to a thread chart.

Why do fittings with the same thread not always fit together?

Because the seal is separate from the thread. JIC and SAE O-ring boss share threads, as do BSPP and JIS 30°, and metric DIN and Komatsu. Their sealing surfaces are different, so they screw together but leak.

Which hydraulic fitting type is best?

For new designs, O-ring connections such as ORFS, O-ring boss and flanges are preferred because they seal reliably under vibration. For a repair, the best fitting is the one that matches what the machine was built with.

Can I use an adapter between two fitting types?

Yes. Adapters with a different family on each end are the correct way to join, for example, a BSPP port to a JIC hose. Never force two different families together directly.

Tools and data for the job

Standards referenced

SAE J514 / ISO 8434-2 — 37° flare. SAE J1453 / ISO 8434-3 — O-ring face seal.
ISO 228-1 and ISO 7-1 — BSP parallel and tapered pipe threads. ASME B1.20.1 — NPT.
ISO 8434-1 / DIN 2353 — metric 24° cone. JIS B 8363 — 30° flare hose fittings.
SAE J1926 / ISO 11926 — O-ring boss ports. SAE J518 / ISO 6162 — four-bolt split flanges.

Dimensions are nominal reference values. Confirm against the standard or the fitting manufacturer before ordering.