Hydraulic Fittings & Adapters UK Guide: BSP, JIC, ORFS, NPT & Metric Connections Explained
Updated: 16 September 2026
Correctly identifying a hydraulic fitting requires more than measuring the thread diameter. Thread type, pitch, sealing method, seat form, size and system compatibility all need to be considered before selecting a replacement fitting or adapter.
Hydraulic machinery operating in the UK can contain several different connection standards — sometimes on the same machine. Common families include BSP, JIC, ORFS, NPT and Metric/DIN connections.
This guide explains how these hydraulic connections differ, how to identify them and why apparently similar fittings should never be assumed to be interchangeable.
Start by identifying the thread type and whether it is parallel or tapered. Measure the thread diameter and pitch, then inspect how the connection actually seals — for example on a flare, cone, O-ring face, bonded seal, cutting ring or tapered thread. Do not identify a hydraulic fitting from thread diameter alone.
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Common Hydraulic Fitting Types in the UK
| Connection Family | Typical Feature | Common Sealing Principle |
|---|---|---|
| BSP | British pipe thread family commonly encountered on UK and European equipment | Depends on connection design; may use a sealing face, bonded seal or tapered-thread arrangement |
| JIC | 37° flare connection | Metal-to-metal flare seat |
| ORFS | Flat face with O-ring seal | O-ring face seal |
| NPT | Tapered pipe thread associated particularly with North American equipment | Tapered-thread sealing arrangement with appropriate sealing method |
| Metric / DIN | Metric threads and several connection designs used widely on European machinery | Depends on system; can include O-rings, cone seats or tube fitting arrangements |
Two hydraulic fittings can appear similar and may even have dimensions that seem close, yet use different thread forms, pitches, seat designs or sealing methods. A connection should be positively identified rather than selected because it appears to screw together.
How to Identify a Hydraulic Fitting
A systematic identification process is safer and more reliable than trying to recognise a fitting visually.
1. Check Whether the Thread Is Parallel or Tapered
Parallel threads maintain substantially the same diameter along their threaded length. Tapered threads change diameter along the thread.
This distinction immediately helps narrow the possible connection family.
2. Measure the Thread Diameter
Use suitable measuring equipment such as calipers to obtain the thread diameter.
Remember that the measured outside diameter does not necessarily equal the nominal description of the connection.
3. Determine the Thread Pitch
A thread-pitch gauge can help establish either:
- Threads per inch for applicable imperial thread systems
- Metric pitch in millimetres for metric threads
Diameter and pitch should be considered together.
4. Inspect the Sealing Method
Determine where the connection is intended to seal.
Look for features such as:
- Flared metal seat
- Cone seat
- Flat O-ring face
- Port O-ring
- Bonded seal
- Cutting ring
- Tapered thread
5. Inspect the Seat or Connection Form
The seat geometry can be critical. JIC connections, for example, use a 37° flare, while other hydraulic connection families use different sealing arrangements.
Do not assume two cone-shaped fittings are compatible simply because they look similar.
6. Compare Against Reliable Identification Data
Once the physical features have been established, compare the measurements and connection form against the relevant manufacturer’s technical information or a reliable fitting identification reference.
BSP Hydraulic Fittings
BSP — British Standard Pipe connections are widely encountered on hydraulic equipment operating in the UK and Europe.
The two terms commonly encountered are:
- BSPP — parallel thread
- BSPT — tapered thread
The presence of a BSP thread alone does not tell you exactly how the connection seals.
Depending on the fitting and port design, sealing may occur through a sealing face, bonded seal or tapered-thread arrangement.
Common BSP Identification Mistakes
- Assuming every BSP connection seals on the thread
- Confusing parallel and tapered versions
- Identifying the connection by diameter alone
- Ignoring the sealing face
- Reusing damaged sealing components
- Assuming another pipe-thread family is interchangeable
A fitting that threads into a port is not necessarily the correct fitting for that port.
JIC Hydraulic Fittings
JIC connections use a 37° flare to create the sealing interface.
They are commonly encountered on mobile, construction, agricultural and industrial hydraulic equipment.
The thread pulls the mating flare surfaces together, but the sealing function is primarily associated with the flare interface rather than simply the thread itself.
What to Inspect on a JIC Connection
- Flare seating surface
- Thread condition
- Evidence of scoring
- Deformation
- Corrosion
- Alignment
- Correct mating connection
A damaged seating surface can leak even when the thread appears undamaged.
One of the most useful fitting-identification questions is not simply “What thread is this?” but “Where is this connection designed to seal?” The answer can quickly separate fittings that otherwise look very similar.
ORFS Hydraulic Fittings
ORFS means O-Ring Face Seal.
The connection uses an O-ring at the face of the fitting to create the seal when the mating faces are assembled correctly.
ORFS connections are used in many hydraulic applications where a positive sealed connection is required.
What to Inspect on ORFS
- Correct O-ring specification
- O-ring condition
- Face condition
- O-ring groove
- Threads
- Alignment
- Evidence of contamination or damage
A damaged O-ring should not simply be reused because the fitting itself appears serviceable.
Likewise, fitting a new O-ring will not correct a damaged sealing face.
NPT Hydraulic Connections
NPT — National Pipe Taper — is commonly associated with North American equipment and may therefore be encountered on imported machinery, attachments and hydraulic components operating in the UK.
NPT uses a tapered thread arrangement.
It should not be assumed to be interchangeable with BSP tapered connections.
BSP and NPT connections can sometimes look deceptively similar. Forcing incompatible threads together can damage the fitting or port and still fail to create the intended seal. Positively identify both connections and use the correct adapter where different systems need to be joined.
Metric Hydraulic Fittings
Metric hydraulic connections are widely used on European industrial and mobile machinery.
However, “metric fitting” is not one single connection type.
Metric threads appear in several hydraulic connection systems, so thread diameter and pitch alone do not establish the complete fitting.
The sealing arrangement must also be identified.
DIN Tube Fittings
Metric tube fitting systems commonly associated with DIN/ISO designs are frequently encountered on European machinery.
Depending on the system, connections can incorporate tube, nut and cutting-ring or other sealing arrangements.
Light and heavy series components are selected according to the relevant tube and connection specification.
Components should not be interchanged merely because the threads appear compatible.
ISO 6149 Hydraulic Ports
ISO 6149-style ports use a metric straight thread and an elastomeric sealing arrangement at the port.
This is different from a connection that depends on a flare or tapered thread to create its seal.
When inspecting this type of connection, check:
- Thread condition
- O-ring condition
- Sealing area
- Correct fitting type
- Correct size and pitch
BSP vs JIC: What Is the Difference?
BSP and JIC are different connection systems.
| Feature | BSP | JIC |
|---|---|---|
| Connection family | British pipe thread | 37° flare connection |
| Thread arrangement | Parallel or tapered forms exist | Straight-thread flare connection |
| Primary sealing principle | Depends on specific BSP connection design | 37° metal flare interface |
| Interchangeable? | No — identify and adapt correctly where required. | |
ORFS vs JIC: Which Should You Use?
There is no universal rule that ORFS is always better than JIC or vice versa.
They use different sealing principles and the appropriate connection depends on factors such as:
- Machine design
- Existing hydraulic system
- OEM specification
- Operating pressure
- Temperature
- Fluid
- Vibration
- Environment
- Maintenance requirements
- Component availability
Where an existing machine has been designed around a particular connection system, changing connection type should be treated as an engineering decision rather than simply choosing whichever fitting is available.
Understanding Hydraulic Hose Dash Sizes
Many hydraulic hose ranges use dash numbers to describe nominal hose size.
For many commonly used hose ranges, the dash number relates to sixteenths of an inch.
| Common Dash Size | Approximate Nominal Hose Bore |
|---|---|
| -04 | 1/4 inch |
| -06 | 3/8 inch |
| -08 | 1/2 inch |
| -12 | 3/4 inch |
| -16 | 1 inch |
This convention should not be used blindly across every product family. Always confirm the hose and manufacturer’s specification.
See our hydraulic hose sizes guide for more detail.
Fitting Size Is Not Necessarily Hose Size
This is another common source of identification errors.
A hose assembly can contain:
- A nominal hose bore size
- A fitting thread size
- A fitting connection type
- A particular sealing interface
These pieces of information describe different parts of the assembly.
Do not identify the hose itself solely by measuring the fitting thread.
Hydraulic Adapters: What Do They Do?
A hydraulic adapter allows two suitable but different hydraulic connections to be joined.
Adapters can be used to:
- Change thread type
- Change connection size
- Join different connection families
- Change orientation
- Provide a suitable interface between components
For example, a correctly specified adapter may be used where equipment contains one connection family and the replacement component uses another.
However, every additional adapter introduces another interface into the hydraulic circuit.
Unnecessary chains of adapters can create more potential leak points and make installations harder to support and maintain.
Read our dedicated hydraulic adapters guide.
Can You Mix Hydraulic Fitting Manufacturers?
Do not assume hydraulic hose and fitting components from different manufacturers are interchangeable simply because their nominal dimensions appear compatible.
For hose assemblies in particular, hose, fitting and crimp specifications need to form an approved and validated system.
Crimp dimensions and component compatibility are determined by the relevant hose and fitting system.
Completely Hydraulic is an official Alfagomma distributor, supporting hose and fitting supply through its trade counters and engineering operations.
How to Select the Correct Hydraulic Fitting
Correct selection should consider the complete application.
Important factors include:
- Connection standard
- Thread type
- Thread pitch
- Size
- Sealing method
- Operating pressure
- Fluid compatibility
- Temperature
- Environment
- Hose, pipe or tube compatibility
- Movement and vibration
- Corrosion exposure
- Installation space
- Manufacturer requirements
The fitting needs to be suitable for the system — not merely capable of being screwed into the connection.
Hydraulic Fitting Pressure Ratings
Pressure capability should be confirmed for the actual fitting, adapter and complete hydraulic assembly being used.
Do not assume that all fittings of the same thread size have the same working-pressure capability.
The usable rating can depend on:
- Connection type
- Size
- Material
- Manufacturer
- Component series
- Assembly design
- Temperature
- Application
The complete assembly should be selected for the hydraulic system’s requirements.
Why Hydraulic Fittings Leak
A leak at a hydraulic connection does not automatically mean the fitting simply needs tightening.
Possible causes include:
- Incorrect fitting type
- Damaged sealing face
- Damaged O-ring or seal
- Damaged threads
- Contamination on the sealing surface
- Misalignment
- Side loading
- Incorrect installation
- Under-tightening
- Over-tightening
- Vibration
- Corrosion
- Damaged connected hose or tube
Repeatedly tightening a leaking hydraulic connection can damage threads, seats, seals or components. If the connection continues to leak, identify the fitting and sealing method and inspect the mating components before deciding what needs replacing.
When Should a Hydraulic Fitting Be Replaced?
A fitting or associated sealing component may require replacement when inspection finds:
- Damaged threads
- Cracking
- Deformation
- Significant corrosion
- Damaged flare or seat
- Damaged sealing face
- Damaged O-ring groove
- Persistent leakage caused by component damage
Seals such as O-rings or bonded seals should also be replaced where required using components appropriate to the connection and hydraulic fluid.
Do not reuse a damaged fitting simply because it can still be physically assembled.
Correct Hydraulic Fitting Installation
Correct fitting identification is only part of the job. Installation also affects reliability.
Good installation practice includes:
- Keeping sealing surfaces clean
- Checking threads before assembly
- Using the correct sealing components
- Avoiding cross-threading
- Following appropriate manufacturer tightening or torque requirements
- Avoiding hose twist
- Avoiding side loading
- Supporting pipework and hoses appropriately
- Checking routing through the machine’s movement
Over-tightening can damage a connection just as under-tightening can allow leakage.
Hydraulic Fittings & Hose Routing
The fitting at the end of a hose should not be considered independently from the hose route.
Poor routing can place unwanted forces onto the connection.
Problems can include:
- Hose twist
- Side loading at the fitting
- Excessively tight bends close to the end fitting
- Abrasion
- Insufficient allowance for machine movement
- Heat exposure
Correct routing can reduce stress on both the hose and its connections.
See our hydraulic hose routing guide.
Hydraulic Fitting Identification at the Trade Counter
If you cannot positively identify a hydraulic fitting, Completely Hydraulic’s trade counters can help with hose, fitting and adapter requirements.
Where practical, bringing the original fitting, hose assembly or component can provide useful identification information.
Photographs and machine information may also help, particularly when the connection cannot easily be removed.
Completely Hydraulic has trade counters in:
- Essex — Harlow
- London — Dagenham
- Kent — Belvedere
- Heathrow — Hayes
Visit our hydraulic trade counter information.
While-You-Wait Hydraulic Hose Assemblies
Where the hose and connections can be correctly identified and suitable components are available, replacement hydraulic hose assemblies can be manufactured at Completely Hydraulic’s trade counters.
Correct hose assembly manufacture requires the hose and end fittings to form a suitable system and to be assembled according to the applicable specification.
Read about our while-you-wait hydraulic hose service.
On-Site Hydraulic Fitting Support
When machinery cannot conveniently be brought to a trade counter, Completely Hydraulic also provides 24/7 mobile hydraulic engineering.
Mobile engineers can support suitable requirements involving:
- Failed hydraulic hoses
- Fitting identification
- Replacement hose assemblies
- Adapters
- Hydraulic leaks
- Connection problems
- System diagnosis
Specialist or unusual components may need to be sourced, so not every possible fitting can be carried on every mobile vehicle.
Hydraulic Fitting Safety
High-pressure hydraulic fluid can penetrate the skin and cause a serious injection injury. Equipment should be appropriately isolated and stored hydraulic pressure safely relieved before a fitting, hose or connection is inspected or dismantled.
Frequently Asked Questions
How do I know what hydraulic fitting I have?
Identify whether the thread is parallel or tapered, measure its diameter and pitch, and inspect the connection’s sealing method and seat form. Compare these features against reliable fitting identification information rather than using thread diameter alone.
What are the most common hydraulic fittings in the UK?
Common connection families encountered on UK machinery include BSP, JIC, ORFS and metric/DIN connections. NPT is also encountered, particularly on North American or imported equipment.
What is the difference between BSP and JIC?
BSP is a British pipe-thread family with parallel and tapered forms, while JIC is a 37° flare connection. They are different systems and should not be treated as interchangeable.
Are BSP and NPT the same?
No. BSP and NPT are different thread systems. Similar-looking threads should be positively identified rather than forced together.
What does ORFS mean?
ORFS means O-Ring Face Seal. The connection uses an O-ring at the face of the fitting to create the sealing interface.
Are all metric hydraulic fittings the same?
No. Metric threads are used across several hydraulic connection systems. Diameter and pitch alone do not identify the complete fitting because the sealing method and connection design must also be established.
Can I identify a hydraulic fitting by thread diameter?
Not reliably. Thread diameter is only one measurement. Pitch, thread form, sealing method, seat geometry and connection type also need to be considered.
Can I mix BSP and NPT fittings?
They should not be treated as directly interchangeable. If two different connection systems need to be joined, identify both correctly and use an appropriate adapter.
Why is my hydraulic fitting leaking?
Possible causes include an incorrect fitting, damaged seal or sealing face, damaged threads, contamination, misalignment, incorrect installation, corrosion or problems with the connected hose or tube.
Should I just tighten a leaking hydraulic fitting?
No. Tightening without identifying the cause can damage the connection. The fitting, sealing method and mating components should be inspected first.
Can Completely Hydraulic identify my hydraulic fitting?
Completely Hydraulic supplies hydraulic hoses, fittings and adapters through its trade counters and mobile engineering service. Bringing the original component or accurate measurements can help with identification.
Get Priority Hydraulic Support & Trade Pricing
Jump the queue. Reduce downtime. Pay less for parts, labour and callouts.
✔ Priority response
✔ Lower rates day & night
✔ Trade discounts on parts
✔ 30-day credit terms (approved accounts)
Need Help Identifying a Hydraulic Fitting?
Bring your hose or fitting to a Completely Hydraulic trade counter, or contact our team for hydraulic fitting, adapter and hose support.