When choosing or replacing a quick coupling, one of the most important factors is selecting the correct thread type and size. Mismatched threads can cause leaks, damage components, or create unsafe working conditions.
In this guide, we’ll break down the most common thread types used in hydraulic and pneumatic quick couplings, their key characteristics, dimensional charts, and tips on identification.
Why Threads Matter in Quick Couplings
Threads connect the quick coupling to hoses, fittings, valves, and other system components. Choosing the correct thread ensures:
- Leak-free connections
- Mechanical compatibility
- Compliance with regional and industry standards
Common Thread Types in Quick Couplings
1. BSPP (British Standard Pipe Parallel) – G Thread
- Thread type: Parallel (straight)
- Sealing method: Uses a bonded washer or O-ring face seal (ORFS)
- Common in: Europe, Asia, Australia
- Standard: ISO 228
2. BSPT (British Standard Pipe Taper) – R Thread
- Thread type: Tapered
- Sealing method: Threads seal by metal-to-metal contact
- Common in: UK, Asia
- Standard: ISO 7-1 / BS 21
3. NPT (National Pipe Tapered)
- Thread type: Tapered
- Sealing method: Thread interference (often with PTFE tape or sealant)
- Common in: United States and Canada
- Standard: ANSI/ASME B1.20.1
4. SAE (Straight Thread O-Ring Boss – ORB)
- Thread type: Straight
- Sealing method: O-ring inside a machined groove
- Common in: Hydraulic systems in North America
- Standard: SAE J514
5. UNF (Unified National Fine)
- Thread type: Straight
- Sealing method: Usually with an O-ring or gasket
- Used in: North American fluid power systems
- Standard: ANSI B1.1
6. JIC (Joint Industry Council 37° Flare)
- Thread type: UNF thread with 37° flare sealing
- Sealing method: Metal-to-metal flare (no O-ring needed)
- Common in: Hydraulic applications worldwide
- Standard: SAE J514 / ISO 8434-2
7. Metric Threads
- Thread type: Straight or tapered
- Sealing method: Depends on design (O-ring, flare, metal-to-metal)
- Common in: Automotive and European machinery
- Standard: ISO 261 / ISO 6149
Thread Identification Chart
| Thread Type | Common Sizes (in Couplings) | Example Size Marking | Pitch (mm) or TPI | Sealing Style |
|---|---|---|---|---|
| BSPP | 1/4″ to 1 1/2″ | G 1/2 | 14 TPI | Washer or O-ring |
| BSPT | 1/4″ to 1 1/2″ | R 3/8 | 19 TPI (1/4″) | Thread interference |
| NPT | 1/8″ to 2″ | 1/2″-14 NPT | 14 TPI | Thread interference |
| SAE (ORB) | 7/16″ to 1 5/16″ | 9/16″-18 ORB | 18 TPI | O-ring Boss |
| UNF | 7/16″ to 1 5/16″ | 3/4″-16 UNF | 16–20 TPI | O-ring or flare |
| JIC | 1/8″ to 1 1/2″ | 3/4″-16 JIC | 16 TPI | 37° flare |
| Metric | M10 to M33 | M22x1.5 | 1.5 mm pitch | Depends on design |
How to Identify Thread Type
Step-by-Step:
- Measure the Outside Diameter (OD) of the male thread or Inside Diameter (ID) of the female thread.
- Determine the thread pitch – use a pitch gauge or compare with known threads.
- Check for taper – tapered threads get narrower toward the tip.
- Look at the sealing method:
- O-ring present? Likely ORB or SAE.
- Flare? Likely JIC.
- Tapered metal thread? Could be NPT or BSPT.
- Flat washer or face seal? Likely BSPP.
Thread Matching Tips
- Do not mix BSP and NPT threads—even if the size seems similar, the pitch and angle differ.
- Use thread sealant (like PTFE tape) only on taper threads (NPT, BSPT).
- Use O-rings or bonded washers for sealing parallel threads (BSPP, ORB).
- Always use a thread gauge when uncertain.
Quick Coupling Thread Selection Guide
| Application | Recommended Thread Type |
|---|---|
| North American Hydraulics | NPT, SAE, JIC, UNF |
| European Machinery | BSPP, Metric |
| Pneumatic Systems | BSPP, NPT, Metric |
| Agricultural Equipment | NPT, ORB, BSPP |
| Automotive & Mobile Hydraulics | JIC, ORB, Metric |
Conclusion
Thread selection is a key detail when working with quick couplings. With options like BSP, NPT, SAE, JIC, UNF, and Metric, it’s easy to feel overwhelmed—but once you understand the basics of thread type, sealing method, and sizing standards, the process becomes much clearer.
Whether you’re building a new system or replacing worn fittings, taking time to identify the correct thread ensures leak-free performance and safe operation.