Hydraulic Fittings & Adapters UK & Europe: BSP, JIC, ORFS, Metric & Flange Connections
Updated: 19 September 2026
Hydraulic fittings and adapters connect hoses, tubes, pipes, valves, cylinders, pumps and other components throughout a hydraulic system. The difficult part is that fittings which look similar can use completely different threads, sealing methods and seat designs.
Across UK and European machinery, commonly encountered connection families include BSP, JIC, ORFS and metric/DIN connections, alongside flanges and equipment-specific connection types.
Do not identify a hydraulic fitting by thread diameter alone. Check the thread type, diameter, pitch, sealing method, seat form or angle, connection size and application. BSP, JIC, ORFS and metric fittings can appear similar but are not automatically interchangeable.
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Common Hydraulic Fitting Types in the UK & Europe
| Connection Family | Typical Identification Feature | Important Point |
|---|---|---|
| BSP | British Standard Pipe thread family | BSPP and BSPT should not be treated as the same connection |
| JIC | 37° flare sealing arrangement | The flare seat forms the sealing interface |
| ORFS | O-ring face seal | Condition of the face and O-ring is important |
| Metric / DIN | Metric thread and defined sealing arrangement | A metric thread alone does not fully identify the connection |
| NPT | Tapered pipe thread | May be encountered on imported equipment |
| Flange | Bolted flange connection | Commonly used where the system design requires a flange connection |
BSP Hydraulic Fittings
BSP — British Standard Pipe — connections are widely encountered on hydraulic equipment in the UK, but seeing a threaded connection on British machinery does not automatically mean it is BSP.
Two terms commonly encountered are:
- BSPP — British Standard Pipe Parallel
- BSPT — British Standard Pipe Taper
The distinction matters because the thread and sealing arrangement need to match the component being connected.
A BSP connection may seal using a separate sealing feature rather than simply relying on the threads themselves, depending on the particular fitting design.
BSP connections are widespread in UK hydraulic systems, but UK machinery can also contain JIC, ORFS, metric, NPT, flange and manufacturer-specific connections. Always identify the actual connection fitted to the machine.
JIC Hydraulic Fittings
JIC hydraulic fittings use a 37-degree flare sealing arrangement.
The connection is commonly found across mobile, industrial and imported hydraulic equipment.
With a JIC connection, the mating flare surfaces are an important part of the seal. Damage, contamination or deformation at the seating surface can therefore contribute to leakage even if the threads themselves appear undamaged.
JIC fittings should not be chosen simply because an application operates at high pressure. The complete fitting specification must be suitable for the system’s pressure, fluid, temperature, duty and connected hose or tube.
ORFS — O-Ring Face Seal Fittings
ORFS stands for O-Ring Face Seal.
Unlike a flare connection, an ORFS fitting incorporates an O-ring at the mating face to form the seal when the connection is assembled correctly.
ORFS connections are used in many hydraulic applications where a reliable sealed joint is required.
When inspecting an ORFS connection, check:
- The O-ring
- The sealing face
- Threads
- Contamination
- Physical damage
- Alignment of the connected components
An old, damaged or incorrect O-ring should not simply be reused because the fitting can still be screwed together.
Metric & DIN Hydraulic Fittings
Metric hydraulic connections are widely used throughout European machinery and equipment.
However, the word metric describes the thread measurement system — it does not by itself tell you how the connection seals.
Correct identification may require checking:
- Thread outside diameter
- Thread pitch
- Male or female connection
- Seat or sealing form
- Tube outside diameter where relevant
- Series or fitting specification
Two fittings can therefore both have metric threads and still be incompatible.
DIN Hydraulic Connections
DIN-style tube connections are commonly encountered on European industrial and mobile hydraulic equipment.
Depending on the system, these may incorporate cutting rings, sealing cones, O-rings or other defined connection arrangements.
Identification should therefore be based on the complete connection rather than assuming that any fitting with a metric thread is an interchangeable DIN fitting.
NPT Hydraulic Fittings
NPT connections may also be encountered in UK and European hydraulic systems, particularly on imported machinery and components.
NPT is a tapered thread system and should not be confused with BSP simply because both are pipe-thread connection families.
Attempting to join incompatible pipe threads can damage components and produce an unreliable connection.
Hydraulic Flange Connections
Flange connections are used in many hydraulic systems where the circuit and component design calls for a bolted connection.
They can be found on pumps, motors, valves, manifolds and larger hydraulic lines.
A flange connection should be identified using its complete specification, including:
- Flange type
- Size
- Pressure series or rating
- Bolt arrangement
- Port dimensions
- Sealing arrangement
It is therefore unsafe to assume that two flanges are interchangeable merely because their physical dimensions appear similar.
Komatsu & Equipment-Specific Hydraulic Connections
Construction and heavy equipment can contain connection arrangements associated with particular manufacturers or equipment families.
Terms such as Komatsu fitting are often used in the hydraulic trade, but the machine manufacturer alone should not be used as the complete fitting specification.
Equipment may contain several connection standards across different circuits, components or production years.
When replacing a fitting on construction equipment, identify the actual thread and sealing arrangement rather than relying only on the machine badge.
What Is a Hydraulic Adapter?
A hydraulic adapter is a component used to connect two hydraulic interfaces where a direct connection is not available or appropriate.
Adapters may be used to:
- Change connection type
- Change connection size
- Join male and female interfaces
- Change orientation
- Connect hose to pipe, tube, valve or another component
- Transition between suitable connection standards
For example, an engineered hydraulic circuit may require an adapter between a BSP port and another suitable connection type.
Fitting vs Adapter: What’s the Difference?
| Hydraulic Fitting | Hydraulic Adapter |
|---|---|
| Forms a hydraulic connection | Provides an interface between suitable connections |
| May be attached to hydraulic hose or tube | Often connects two existing fitting or port arrangements |
| Can incorporate a defined sealing face | Can transition between compatible sizes or standards |
Do Hydraulic Adapters Increase the Risk of Leaks?
A correctly specified and installed hydraulic adapter is a normal engineering component.
However, every additional connection introduces another interface into the circuit.
Unnecessary chains of adapters can:
- Create additional potential leak points
- Increase component length
- Introduce additional mechanical loading
- Make servicing more complicated
- Increase the opportunity for incorrect connections
Adapters are useful engineering components, but several adapters joined together should not be used simply to make incompatible components fit. Where possible, use a correctly specified connection arrangement for the application.
How Do You Measure a Hydraulic Fitting?
Correct fitting identification normally requires more than one measurement.
A useful identification process can include:
- Determine whether the connection is male or female.
- Measure the thread diameter.
- Determine the thread pitch.
- Check whether the thread is parallel or tapered.
- Identify the sealing method.
- Inspect the seat or face.
- Confirm the fitting size and application.
A thread gauge and suitable measuring tools can help, but measurement still needs to be interpreted against the relevant connection specification.
Why Thread Diameter Alone Is Not Enough
One of the most common fitting-identification mistakes is measuring a thread and assuming that measurement identifies the connection.
It does not.
Different connection families may have similar-looking diameters while using different:
- Thread pitches
- Thread forms
- Seat angles
- Sealing faces
- O-rings
- Taper arrangements
This is why forcing together two connections that appear to be almost the same can damage both parts.
How Do Hydraulic Fittings Seal?
Hydraulic fittings do not all seal in the same way.
Depending on the connection, sealing can occur through:
- A flare or cone seat
- An O-ring
- A face seal
- A bonded or separate sealing element
- A defined tapered thread arrangement
- Another engineered sealing interface
Understanding where the connection is supposed to seal is an important part of diagnosing a leaking fitting.
Why Is My Hydraulic Fitting Leaking?
A leaking hydraulic fitting does not automatically mean that it simply needs tightening.
Possible causes include:
- Damaged sealing face
- Damaged or missing O-ring
- Incorrect seal
- Loose connection
- Overtightening
- Damaged threads
- Incorrect fitting combination
- Contamination on the sealing surface
- Corrosion
- Misalignment or side loading
- Movement or vibration
- Damage to the connected hose or tube
If a hydraulic fitting continues to leak, investigate the connection. Excessive tightening can damage threads, sealing faces, O-rings or connected components and may make the original problem worse.
Can You Mix Different Hydraulic Fitting Standards?
Different fitting standards should not be joined simply because the threads appear to engage.
A connection must be deliberately designed or adapted using components suitable for both interfaces.
Forcing incompatible threads together can:
- Damage threads
- Damage sealing surfaces
- Create leakage
- Produce an unreliable joint
- Make later identification more difficult
Where two different connection families genuinely need to be joined, use an appropriately specified hydraulic adapter.
Can Hydraulic Hose Fittings From Different Manufacturers Be Mixed?
Hydraulic hose and fitting compatibility is particularly important when producing hose assemblies.
Components from different hose and fitting systems should not be mixed merely because they appear physically compatible.
The hose, fitting and assembly method need to form an approved or appropriately validated combination for the intended application.
Completely Hydraulic is an official Alfagomma distributor, providing access to hydraulic hose and associated fluid-transfer products through our engineering and trade-counter network.
How Do You Choose the Correct Hydraulic Fitting?
The correct fitting is determined by the complete hydraulic application rather than one measurement.
Selection should consider:
- Connection standard
- Thread type and pitch
- Sealing method
- Fitting size
- System working pressure
- Fluid compatibility
- Operating temperature
- Hose, pipe or tube specification
- Movement and vibration
- Environment
- Corrosion exposure
- Installation access
- Maintenance requirements
Are Higher-Pressure Fittings Always Better?
No.
A hydraulic fitting should be suitable for the actual circuit and compatible with the other components.
Installing a component with a higher nominal pressure capability does not compensate for:
- An incompatible thread
- An incorrect sealing method
- Wrong hose selection
- Poor installation
- Incorrect assembly
- Damaged components
The hydraulic connection needs to work as a complete system.
Hydraulic Fittings for Replacement Hoses
When replacing a hydraulic hose, both end connections need to be identified correctly.
Useful information includes:
- Complete original hose assembly
- Hose layline
- Fitting orientation
- Thread and seat details
- Hose length
- Machine make and model
- Application
- Routing
Our Hydraulic Hose Fittings Explained guide provides further information specifically about hose-end connections.
Where Can I Buy Hydraulic Fittings & Adapters?
Completely Hydraulic operates four hydraulic trade counters in:
- Harlow — Essex
- Dagenham — London
- Belvedere — Kent
- Hayes — Heathrow
Customers can bring an existing hose, fitting or adapter into a trade counter to help with identification where practical.
Visit our Hydraulic Trade Counter guide or view all four Completely Hydraulic trade counters.
What Should I Bring to the Trade Counter?
If you need help identifying a hydraulic connection, bring as much of the original assembly as practical.
Useful items include:
- The original fitting
- The complete hose assembly
- The mating component where practical
- Machine make and model
- Part numbers or manufacturer markings
- Clear photographs
- Measurements
- Known operating information
This can be considerably more reliable than trying to identify a fitting from a single thread measurement.
Need a Hydraulic Fitting Replaced on Site?
If machinery is immobilised and the hydraulic hose or connection cannot be safely removed and brought to a trade counter, Completely Hydraulic also provides 24/7 mobile hydraulic engineering support.
Mobile engineers can assess suitable hydraulic hose and connection failures on site and produce replacement hose assemblies where the required compatible components are available.
Frequently Asked Questions
What are the most common hydraulic fitting types in the UK?
BSP is widely encountered in UK hydraulic equipment, alongside JIC, ORFS, metric/DIN, NPT, flange and other connection types. The actual connection fitted to the machine should always be identified rather than assuming its type from location alone.
What does BSP mean on a hydraulic fitting?
BSP means British Standard Pipe. BSPP refers to parallel threads and BSPT refers to tapered threads. The complete connection and sealing arrangement should be identified before selecting a replacement.
What does JIC mean?
JIC is a hydraulic connection family commonly associated with a 37-degree flare sealing arrangement.
What is an ORFS fitting?
ORFS means O-Ring Face Seal. The connection uses an O-ring at the mating face to create the seal when correctly specified and assembled.
Are metric hydraulic fittings all interchangeable?
No. Two fittings can both use metric threads while having different pitches, sealing methods, seat forms, sizes or specifications. Metric thread measurement alone does not prove compatibility.
Are BSP and NPT hydraulic fittings interchangeable?
No. BSP and NPT are different thread systems and should not be treated as interchangeable simply because some sizes may appear similar.
How do I know what hydraulic fitting I have?
Identify the male or female connection, thread diameter, thread pitch, parallel or tapered form, sealing method, seat or face design and fitting size. Comparing the complete connection is more reliable than thread diameter alone.
Why does my hydraulic fitting still leak after tightening?
The problem may involve a damaged seal, sealing face, thread, incorrect fitting combination, contamination, misalignment, corrosion or another fault. Continuing to tighten the connection can cause further damage.
Can I reuse an old hydraulic fitting?
Reuse depends on the fitting design, condition, compatibility and applicable manufacturer requirements. Damaged threads, sealing faces, O-rings or deformed components should not be reused simply because they still fit together.
Can different hydraulic fitting types be connected?
Different connection families can sometimes be joined using a correctly specified hydraulic adapter designed for both interfaces. Incompatible threads should never be forced together.
Where can I get a hydraulic fitting identified?
Customers can bring hydraulic hoses, fittings and adapters to Completely Hydraulic trade counters in Harlow, Dagenham, Belvedere and Hayes for identification support where practical.
Need a Hydraulic Fitting or Adapter?
Bring the existing fitting or complete hose assembly to one of our hydraulic trade counters — or call us if the machine requires mobile hydraulic support.