Hydraulic Port Thread Specifications
Complete reference for hydraulic fitting and port threads including SAE, JIC, BSPP, metric, and NPT standards with identification guides.
Thread Type Overview
SAE Straight Thread O-Ring Boss (ORB)
Straight (parallel) threads with O-ring seal in machined boss. The O-ring seats on a chamfered surface in the port. Most reliable hydraulic connection - does not rely on thread deformation for sealing. SAE J1926 / ISO 11926.
Seal: O-ring on boss face
Threads: UN/UNF straight
Pressure: Up to 6,000 psi
Use: Ports in manifolds, valves, pumps
SAE 45-Degree Flare (JIC)
37-degree flare angle on tube/hose end mates with 37-degree cone in fitting. Metal-to-metal seal. Most common tube fitting in North America. Can be disassembled and reassembled. SAE J514 / ISO 8434-2.
Seal: 37-degree metal cone
Threads: UN/UNF straight
Pressure: Up to 5,000 psi
Use: Tube and hose connections
BSPP - British Standard Pipe Parallel
Parallel (straight) threads with bonded seal washer or O-ring. Common in European and Asian equipment. Uses Whitworth thread form (55-degree angle). ISO 228-1 / BS 2779.
Seal: Bonded washer or O-ring
Threads: Whitworth parallel
Pressure: Up to 6,000 psi
Use: European equipment ports
Metric Thread O-Ring Face Seal
Metric threads with O-ring face seal. Common on modern European and Japanese equipment. Similar sealing concept to SAE ORB but with metric dimensions. ISO 6149.
Seal: O-ring on face
Threads: Metric ISO
Pressure: Up to 6,000 psi
Use: Modern metric equipment
NPT - National Pipe Taper
Tapered threads that seal by thread interference and deformation. Requires thread sealant (tape or compound). Not recommended for high-pressure hydraulics due to potential leakage and difficulty achieving consistent seal. ANSI/ASME B1.20.1.
Seal: Thread interference + sealant
Threads: 60-degree tapered
Pressure: Up to 3,000 psi (limited)
Use: Legacy, low pressure, pneumatics
BSPT - British Standard Pipe Taper
Tapered threads similar to NPT but with Whitworth thread form (55-degree). Not interchangeable with NPT. Found on older British and some Asian equipment. BS 21.
Seal: Thread interference + sealant
Threads: 55-degree tapered
Pressure: Up to 3,000 psi (limited)
Use: British legacy equipment
SAE Straight Thread O-Ring Boss (ORB)
| Dash Size | Thread | Thread OD (in) | Thread Pitch | O-Ring Size | Hex (in) | Port Depth (in) |
|---|---|---|---|---|---|---|
| -2 | 5/16-24 UNF | 0.3125 | 24 | -902 | 7/16 | 0.28 |
| -3 | 3/8-24 UNF | 0.375 | 24 | -903 | 1/2 | 0.31 |
| -4 | 7/16-20 UNF | 0.4375 | 20 | -904 | 9/16 | 0.34 |
| -5 | 1/2-20 UNF | 0.500 | 20 | -905 | 5/8 | 0.38 |
| -6 | 9/16-18 UNF | 0.5625 | 18 | -906 | 11/16 | 0.41 |
| -8 | 3/4-16 UNF | 0.750 | 16 | -908 | 7/8 | 0.50 |
| -10 | 7/8-14 UNF | 0.875 | 14 | -910 | 1 | 0.56 |
| -12 | 1-1/16-12 UN | 1.0625 | 12 | -912 | 1-1/4 | 0.62 |
| -14 | 1-3/16-12 UN | 1.1875 | 12 | -914 | 1-3/8 | 0.69 |
| -16 | 1-5/16-12 UN | 1.3125 | 12 | -916 | 1-1/2 | 0.75 |
| -20 | 1-5/8-12 UN | 1.625 | 12 | -920 | 1-7/8 | 0.88 |
| -24 | 1-7/8-12 UN | 1.875 | 12 | -924 | 2-1/8 | 1.00 |
| -32 | 2-1/2-12 UN | 2.500 | 12 | -932 | 2-7/8 | 1.25 |
SAE 37-Degree Flare (JIC)
| Dash Size | Tube OD (in) | Thread | Thread OD (in) | Pitch (TPI) | Hex (in) | Seat Angle |
|---|---|---|---|---|---|---|
| -2 | 1/8 | 5/16-24 UNF | 0.3125 | 24 | 7/16 | 37 deg |
| -3 | 3/16 | 3/8-24 UNF | 0.375 | 24 | 1/2 | 37 deg |
| -4 | 1/4 | 7/16-20 UNF | 0.4375 | 20 | 9/16 | 37 deg |
| -5 | 5/16 | 1/2-20 UNF | 0.500 | 20 | 5/8 | 37 deg |
| -6 | 3/8 | 9/16-18 UNF | 0.5625 | 18 | 11/16 | 37 deg |
| -8 | 1/2 | 3/4-16 UNF | 0.750 | 16 | 7/8 | 37 deg |
| -10 | 5/8 | 7/8-14 UNF | 0.875 | 14 | 1 | 37 deg |
| -12 | 3/4 | 1-1/16-12 UN | 1.0625 | 12 | 1-1/4 | 37 deg |
| -14 | 7/8 | 1-3/16-12 UN | 1.1875 | 12 | 1-3/8 | 37 deg |
| -16 | 1 | 1-5/16-12 UN | 1.3125 | 12 | 1-1/2 | 37 deg |
| -20 | 1-1/4 | 1-5/8-12 UN | 1.625 | 12 | 1-7/8 | 37 deg |
| -24 | 1-1/2 | 1-7/8-12 UN | 1.875 | 12 | 2-1/4 | 37 deg |
| -32 | 2 | 2-1/2-12 UN | 2.500 | 12 | 3 | 37 deg |
JIC vs ORB: JIC and ORB share the same thread sizes but different sealing methods. JIC uses a 37-degree metal cone seal; ORB uses an O-ring in a boss. They are NOT interchangeable without adapters.
BSPP - British Standard Pipe Parallel
| Size | Thread OD (in) | Thread OD (mm) | Pitch (TPI) | Pitch (mm) | Hex (mm) | Seal Type |
|---|---|---|---|---|---|---|
| G1/8 | 0.383 | 9.73 | 28 | 0.907 | 14 | Washer/O-ring |
| G1/4 | 0.518 | 13.16 | 19 | 1.337 | 19 | Washer/O-ring |
| G3/8 | 0.656 | 16.66 | 19 | 1.337 | 22 | Washer/O-ring |
| G1/2 | 0.825 | 20.95 | 14 | 1.814 | 27 | Washer/O-ring |
| G5/8 | 0.902 | 22.91 | 14 | 1.814 | 30 | Washer/O-ring |
| G3/4 | 1.041 | 26.44 | 14 | 1.814 | 32 | Washer/O-ring |
| G1 | 1.309 | 33.25 | 11 | 2.309 | 41 | Washer/O-ring |
| G1-1/4 | 1.650 | 41.91 | 11 | 2.309 | 50 | Washer/O-ring |
| G1-1/2 | 1.882 | 47.80 | 11 | 2.309 | 55 | Washer/O-ring |
| G2 | 2.347 | 59.61 | 11 | 2.309 | 70 | Washer/O-ring |
Metric Thread O-Ring Face Seal (ISO 6149)
| Size | Thread | Thread OD (mm) | Pitch (mm) | O-Ring ID (mm) | Hex (mm) | Tube OD (mm) |
|---|---|---|---|---|---|---|
| M10x1 | M10x1 | 10 | 1.0 | 6.07 | 14 | 6 |
| M12x1.5 | M12x1.5 | 12 | 1.5 | 7.65 | 17 | 6, 8 |
| M14x1.5 | M14x1.5 | 14 | 1.5 | 9.25 | 19 | 8, 10 |
| M16x1.5 | M16x1.5 | 16 | 1.5 | 11.0 | 22 | 10, 12 |
| M18x1.5 | M18x1.5 | 18 | 1.5 | 12.5 | 24 | 12 |
| M20x1.5 | M20x1.5 | 20 | 1.5 | 14.0 | 27 | 14, 15 |
| M22x1.5 | M22x1.5 | 22 | 1.5 | 15.6 | 27 | 15, 16 |
| M24x1.5 | M24x1.5 | 24 | 1.5 | 17.0 | 30 | 16, 18 |
| M26x1.5 | M26x1.5 | 26 | 1.5 | 19.0 | 32 | 18, 20 |
| M27x2 | M27x2 | 27 | 2.0 | 20.0 | 32 | 20 |
| M30x2 | M30x2 | 30 | 2.0 | 23.0 | 36 | 22 |
| M33x2 | M33x2 | 33 | 2.0 | 26.0 | 41 | 25 |
| M36x2 | M36x2 | 36 | 2.0 | 28.0 | 46 | 28 |
| M42x2 | M42x2 | 42 | 2.0 | 34.0 | 50 | 30, 32 |
| M48x2 | M48x2 | 48 | 2.0 | 40.0 | 55 | 35, 38 |
NPT - National Pipe Taper
| NPT Size | Threads Per Inch | Major Dia (in) | Drill Size (in) | Thread Length (in) | Taper |
|---|---|---|---|---|---|
| 1/16 NPT | 27 | 0.3125 | 0.242 | 0.261 | 1:16 |
| 1/8 NPT | 27 | 0.405 | 0.332 | 0.264 | 1:16 |
| 1/4 NPT | 18 | 0.540 | 0.438 | 0.402 | 1:16 |
| 3/8 NPT | 18 | 0.675 | 0.562 | 0.408 | 1:16 |
| 1/2 NPT | 14 | 0.840 | 0.703 | 0.534 | 1:16 |
| 3/4 NPT | 14 | 1.050 | 0.922 | 0.546 | 1:16 |
| 1 NPT | 11.5 | 1.315 | 1.156 | 0.683 | 1:16 |
| 1-1/4 NPT | 11.5 | 1.660 | 1.500 | 0.707 | 1:16 |
| 1-1/2 NPT | 11.5 | 1.900 | 1.734 | 0.724 | 1:16 |
| 2 NPT | 11.5 | 2.375 | 2.203 | 0.757 | 1:16 |
NPT Limitations: NPT threads rely on thread deformation for sealing and always require thread sealant. They can develop leaks over time, especially under vibration or thermal cycling. For high-pressure hydraulics, SAE ORB or JIC connections are preferred.
Thread Identification Guide
Step 1: Determine if threads are tapered or parallel (straight).
- Place a straight edge against the threads
- Tapered: Gap increases toward the end
- Parallel: Even gap along entire length
- Place a straight edge against the threads
- Tapered: Gap increases toward the end
- Parallel: Even gap along entire length
Step 2: Measure the thread pitch.
- Use a thread pitch gauge
- Or count threads per inch (TPI)
- Metric threads measured in mm between peaks
- Use a thread pitch gauge
- Or count threads per inch (TPI)
- Metric threads measured in mm between peaks
Step 3: Measure the thread OD.
- Use calipers on male threads
- Measure at the major diameter
- For tapered threads, measure at reference point
- Use calipers on male threads
- Measure at the major diameter
- For tapered threads, measure at reference point
| If You Have... | Thread Type | Key Identifier |
|---|---|---|
| Straight thread + O-ring groove | SAE ORB | O-ring visible, UN thread |
| Straight thread + 37 deg cone | JIC (SAE J514) | 37 deg flare angle |
| Straight thread + flat seat | BSPP | 55 deg Whitworth thread form |
| Straight metric thread + O-ring | Metric (ISO 6149) | Metric pitch, O-ring |
| Tapered thread + 60 deg form | NPT | Tapered, requires sealant |
| Tapered thread + 55 deg form | BSPT | Whitworth tapered |
Common Thread Confusion Points
| Thread A | vs | Thread B | How to Tell Apart |
|---|---|---|---|
| JIC -4 | vs | SAE ORB -4 | Same thread, different seal. JIC has cone; ORB has O-ring boss |
| NPT | vs | BSPT | NPT is 60 deg; BSPT is 55 deg. Pitch differs at same nominal size |
| BSPP | vs | BSPT | BSPP is parallel; BSPT is tapered. Check with straight edge |
| Metric | vs | SAE | Measure pitch in mm vs TPI. Metric uses mm; SAE uses fractions |
| G1/4 BSPP | vs | 1/4 NPT | Different OD: BSPP 0.518"; NPT 0.540". Different pitch: 19 vs 18 TPI |