The British Standard Pipe (BSP) thread is a widely used thread standard for pipe fittings in the UK, Europe, Asia, and many other regions. It is primarily used in water, gas, and hydraulic systems to provide a secure, leak-proof connection. BSP threads come in two variations:
✔ BSPP (British Standard Pipe Parallel, also known as G Thread) – Straight (parallel) threads, requiring a sealing washer or O-ring.
✔ BSPT (British Standard Pipe Tapered, also known as R Thread) – Tapered threads that create a mechanical seal by tightening.
BSP threads are standardized under BS 21, ISO 228-1 (parallel), and ISO 7-1 (tapered).
Key Features of BSP Threads:
✔ Thread Angle: 55° Whitworth thread form (different from NPT’s 60°).
✔ BSPP (Parallel Threads): Used in applications where a gasket or O-ring provides sealing.
✔ BSPT (Tapered Threads): Forms a self-sealing joint through thread interference.
✔ Used in fluid transfer systems, including water, gas, oil, and compressed air lines.
BSPP vs BSPT – Key Differences
| Feature | BSPP (G Thread – Parallel) | BSPT (R Thread – Tapered) |
|---|---|---|
| Thread Shape | Straight (parallel) | Tapered |
| Sealing Method | Requires washer/seal | Self-sealing with thread interference |
| Common Use | Hydraulic fittings, plumbing | Gas lines, high-pressure systems |
| Standard | ISO 228-1 | ISO 7-1, BS 21 |
| Thread Angle | 55° | 55° |
Common Applications of BSP Threads:
- Plumbing & Water Systems (Used in household and industrial piping.)
- Hydraulics & Pneumatics (Found in hydraulic fittings, valves, and air compressors.)
- Oil & Gas Industry (Common in gas pipelines and fuel transfer systems.)
- Irrigation & Agricultural Equipment (Used in water pumps and sprinkler systems.)
- Manufacturing & Machinery (Found in pressure gauges, pumps, and industrial piping.)
BSP Standard Thread Sizes & Dimensions
The following tables provide both inch and metric equivalents for major, pitch, and minor diameters, as well as recommended tap drill sizes for BSPP and BSPT threads.
BSPP (Parallel) Thread Dimensions (Inches)
| Nominal Size | Threads Per Inch (TPI) | Major Diameter (in) | Pitch Diameter (in) | Minor Diameter (in) | Tap Drill Size (in) |
|---|---|---|---|---|---|
| 1/16″ | 28 | 0.2611 | 0.2385 | 0.2194 | 0.2180 |
| 1/8″ | 28 | 0.3839 | 0.3605 | 0.3406 | 0.3400 |
| 1/4″ | 19 | 0.5185 | 0.4826 | 0.4530 | 0.4530 |
| 3/8″ | 19 | 0.6560 | 0.6200 | 0.5890 | 0.5890 |
| 1/2″ | 14 | 0.8250 | 0.7700 | 0.7330 | 0.7330 |
| 3/4″ | 14 | 1.0410 | 0.9860 | 0.9490 | 0.9490 |
| 1″ | 11 | 1.3090 | 1.2490 | 1.2060 | 1.2060 |
BSPT (Tapered) Thread Dimensions (Inches)
| Nominal Size | Threads Per Inch (TPI) | Major Diameter (in) | Pitch Diameter (in) | Minor Diameter (in) | Tap Drill Size (in) |
|---|---|---|---|---|---|
| 1/16″ | 28 | 0.2611 | 0.2418 | 0.2270 | 0.2180 |
| 1/8″ | 28 | 0.3839 | 0.3643 | 0.3490 | 0.3400 |
| 1/4″ | 19 | 0.5185 | 0.4946 | 0.4720 | 0.4530 |
| 3/8″ | 19 | 0.6560 | 0.6320 | 0.6100 | 0.5890 |
| 1/2″ | 14 | 0.8250 | 0.8001 | 0.7780 | 0.7330 |
| 3/4″ | 14 | 1.0410 | 1.0161 | 0.9940 | 0.9490 |
| 1″ | 11 | 1.3090 | 1.2841 | 1.2620 | 1.2060 |
BSPP (Parallel) Thread Dimensions (Metric – mm)
| Nominal Size | Major Diameter (mm) | Pitch Diameter (mm) | Minor Diameter (mm) | Tap Drill Size (mm) |
|---|---|---|---|---|
| 1/16″ | 6.63 | 6.14 | 5.77 | 5.54 |
| 1/8″ | 9.75 | 9.25 | 8.86 | 8.64 |
| 1/4″ | 13.17 | 12.56 | 11.99 | 11.51 |
| 3/8″ | 16.66 | 16.05 | 15.49 | 14.96 |
| 1/2″ | 20.95 | 20.32 | 19.76 | 18.62 |
| 3/4″ | 26.44 | 25.81 | 25.25 | 23.88 |
| 1″ | 33.24 | 32.59 | 32.03 | 30.63 |
BSPT (Tapered) Thread Dimensions (Metric – mm)
| Nominal Size | Major Diameter (mm) | Pitch Diameter (mm) | Minor Diameter (mm) | Tap Drill Size (mm) |
|---|---|---|---|---|
| 1/16″ | 6.63 | 6.14 | 5.77 | 5.54 |
| 1/8″ | 9.75 | 9.25 | 8.86 | 8.64 |
| 1/4″ | 13.17 | 12.56 | 11.99 | 11.51 |
| 3/8″ | 16.66 | 16.05 | 15.49 | 14.96 |
| 1/2″ | 20.95 | 20.32 | 19.76 | 18.62 |
| 3/4″ | 26.44 | 25.81 | 25.25 | 23.88 |
| 1″ | 33.24 | 32.59 | 32.03 | 30.63 |
Related Pipe Thread Standards
- NPT – National Pipe Thread (Tapered pipe thread used in North America.)
- NPS – National Pipe Straight (Parallel-threaded pipes used for specific applications.)
- ISO G Thread (Parallel pipe thread standardized under ISO 228-1.)
- ISO R Thread (Tapered pipe thread standardized under ISO 7-1.)
Important Notice on Standards Validity
This information is for reference purposes only. Users should consult official sources and updated standards to ensure compliance with current regulations. The validity of standards may change over time, so it is recommended to verify them through recognized engineering and standardization organizations (BSI, ISO, ANSI, ASME, etc.).
Check with relevant standardization bodies in your region to confirm whether a specific standard is still valid and applicable. Regulations and industry requirements may vary based on region and application.