In a hydraulic system, the hose is rarely alone. It needs to be connected to a pump, a cylinder, a valve or another component. This is done via couplings and fittings — which are secured using threads. It sounds straightforward, but in practice there are dozens of thread types in use, and not every fitting suits every hose.

This article explains it all: which thread types exist, how to identify them, and which fitting family to use for which hose.

Why thread types matter

Fitting the wrong coupling is one of the most common causes of leaks in hydraulic installations. Two threads can look visually identical yet be fundamentally different: a different profile, a different angle, a different sealing method. If you screw a BSP fitting into a metric-threaded port, it may seem to fit — but you are damaging the thread and the installation will leak sooner or later.

Thread types differ in three ways:

The thread profile (the flank angle: 55° or 60°) The pitch (measured between 2 crests) The sealing method (tapered, flat face, O-ring, metal-to-metal)

The main thread types in hydraulics

BSP — British Standard Pipe

BSP is the standard in Europe and by far the most widely used thread in hydraulic installations on this continent. There are two variants:

BSPP (G): parallel thread. Sealing is achieved via a flat face seal, O-ring or bonded seal in the port. The thread itself does not seal. BSPT (Rc/R): tapered thread. The thread tapers and seals on itself. Used in pipework and at lower pressures.

BSP thread has a Whitworth profile with a 55° flank angle. Recognition: the pitch and outside diameter differ from metric dimensions. A 1/4" BSP has an outside diameter of 13.16 mm, for example.

Metric (DIN) — ISO 8434-1 / DIN 2353

Metric connections are standard in European mechanical engineering and hydraulics. They have a 60° flank angle and seal via a 24° cone — sometimes combined with an O-ring (DKOS, form E) for additional sealing reliability.

Recognition: metric thread is designated as M + diameter, for example M14x1.5. The pitch is always indicated.

JIC / SAE — Joint Industry Council

JIC uses a 37° cone that seals metal-to-metal. The cone itself provides the seal — no ring, no O-ring. The fastening thread is based on UNF (Unified National Fine) with a 60° flank angle.

JIC is the standard in North America and is also found in Europe in mobile hydraulics and high-pressure installations. Recognition: the 37° internal cone in the nut or port is the distinguishing feature.

ORFS — O-Ring Face Seal

ORFS is designed for applications where leak-free connection is a priority. Sealing is achieved via an O-ring on the flat face of the fitting. This makes ORFS particularly suitable for high pressures and environments subject to heavy vibration.

ORFS thread is based on UNF (60°). Recognition: the flat sealing face with O-ring groove in the fitting.

NPT — National Pipe Taper

NPT is a tapered thread with a 60° flank angle, common in North America. The thread seals by its taper — PTFE tape is recommended to ensure a reliable seal. NPT is found in Europe in pneumatics and on imported machinery.

Thread type	Profile	Sealing	Typical use
BSP (G/BSPP)	Whitworth, 55°	Flat face seal, O-ring or PTFE on parallel thread; tapered thread seals on itself	Standard European hydraulics, mechanical engineering, mobile hydraulics
BSPT (Rc/R)	Whitworth, 55°	Tapered — thread seals on itself	Pipework, lower pressures, water installations
Metric (DIN)	60° flank	Cone (24°) + O-ring or cutting ring	European hydraulics, mechanical engineering (DIN 2353/ISO 8434-1)
JIC / SAE (UNF)	Unified, 60°	37° cone metal-to-metal	American and mobile hydraulics, high pressure
ORFS (O-Ring Face Seal)	Unified, 60°	O-ring on flat face — leak-free	High pressure, vibration-sensitive installations
NPT (National Pipe Taper)	Unified, 60°	Tapered — thread seals on itself, PTFE recommended	North America, pneumatics, low-pressure hydraulics

Fitting families at Van de Calseyde

Once you know which thread type you need, the next question is: which fitting family do you use for your hose? At Van de Calseyde, we work with four families, each designed for specific hose standards and pressure classes.

X — Standard hydraulic fittings

The X series is the most versatile family, suitable for braided hoses (EN 853) with 1 or 2 wire layers. For use on 4-wire-layer hoses, the special ferrule S312T is required — the same fitting body, but with an adapted ferrule that handles the higher pressure class.

Hose standard: braided (EN 853) Wire layers: 1 or 2 (standard), 4 (with S312T ferrule) Technique: skive or non-skive, depending on the ferrule Application: standard hydraulics, mechanical engineering, agriculture

DS — No-skive for spiral hoses

The DS series is developed for spiral hoses (EN 856) and offers the advantage of no-skive assembly: there is no need to strip the outer cover of the hose. This speeds up assembly and reduces the risk of errors. The DS series can also be used on braided hoses, but the UDS ferrule is then mandatory.

Hose standard: spiral (EN 856), also braided with UDS ferrule Wire layers: 4 or more Technique: no-skive (no stripping) Application: heavy hydraulics, higher flow, fast assembly

HP — Interlock for high pressure

The HP series is the choice for the most demanding applications. The Interlock technique requires both the inner and outer cover of the hose to be stripped. This provides a mechanically very strong connection. A key advantage: the same fitting body is used for both 4- and 6-wire-layer hoses — only the ferrule differs.

Hose standard: spiral (EN 856) Wire layers: 4 or 6 (separate ferrule per class, same fitting body) Technique: Interlock — strip both inner and outer cover Application: very high pressure, heavy-duty applications, mining, offshore

J — One-piece fittings

The J series consists of one-piece fittings where ferrule and fitting body are integrated. This makes assembly fast and compact. The J family is compatible with braided and spiral hoses with 2 or 4 wire layers.

Hose standard: braided or spiral Wire layers: 2 or 4 Technique: skive, one-piece (integrated ferrule) Application: fast assembly, compact installations

Family	Hose standard	Wire layers	Ferrule	Technique	Application
X	Braided (EN 853)	1 or 2	Standard / S312T for 4 layers	Skive / non-skive	Standard hydraulics, mechanical engineering, agriculture
X	Spiral (with S312T)	4	S312T (mandatory)	Non-skive	Higher pressure
DS	Spiral (EN 856)	4 or more	Standard DS ferrule	Non-skive	Heavy hydraulics, higher flow
DS	Braided (with UDS)	1 or 2	UDS (special ferrule)	Non-skive	Flexible use on braided hose
HP	Spiral (EN 856)	4 or 6	Separate ferrule per wire layer	Interlock (strip inner + outer)	Very high pressure, heavy-duty
J	Braided or spiral	2 or 4	Integrated (one-piece)	Non-skive	Fast assembly, compact installation

How to identify an unknown thread type

In practice, you regularly encounter fittings without documentation. Here is how to proceed:

Measure the outside diameter of the thread accurately with a calliper. Count the number of threads over a length of 1 inch (25.4 mm) — this gives you the TPI (threads per inch). Check the flank angle if possible: 55° points to BSP/Whitworth, 60° to metric, JIC, ORFS or NPT. Look at the sealing method: flat face or O-ring = BSPP or ORFS; cone in the port = metric or JIC; tapered thread = BSPT or NPT. If in doubt: bring the fitting to our showroom. We identify the thread type on the spot and advise which fitting you need.

On page 18 of our catalogue, you will find a handy overview of the most common thread types, including pitch, diameters, and threads per inch.

Conclusion

Thread types and fitting families are not a minor detail — they determine whether your installation remains leak-free, can handle the correct pressure class, and stays reliable over time. The combination of the right thread type, the right fitting family and the right ferrule is the foundation of a correct hydraulic connection.

Do you have a specific project or an unknown fitting? Contact us — we will help you make the right choice.