TradeCalculator.co.uk
BSP Pipe Thread Sizes — British Standard Pipe
Complete BSP (British Standard Pipe) thread reference including parallel (BSPP/G) and taper (BSPT/R) thread dimensions, TPI, major diameters and tapping drill sizes.
BSP Thread Dimensions — Parallel (BSPP / G)
Reference: BS EN ISO 228-1. Thread angle 55° (Whitworth form).
| Nominal Size | TPI | Major OD (mm) | Minor ID (mm) | Pitch (mm) | Tapping Drill (mm) |
|---|---|---|---|---|---|
| 1/8" | 28 | 9.728 | 8.566 | 0.907 | 8.6 |
| 1/4" | 19 | 13.157 | 11.445 | 1.337 | 11.5 |
| 3/8" | 19 | 16.662 | 14.950 | 1.337 | 15.0 |
| 1/2" | 14 | 20.955 | 18.631 | 1.814 | 18.6 |
| 3/4" | 14 | 26.441 | 24.117 | 1.814 | 24.1 |
| 1" | 11 | 33.249 | 30.291 | 2.309 | 30.3 |
| 1 1/4" | 11 | 41.910 | 38.952 | 2.309 | 39.0 |
| 1 1/2" | 11 | 47.803 | 44.845 | 2.309 | 44.8 |
| 2" | 11 | 59.614 | 56.656 | 2.309 | 56.7 |
BSP Taper Thread (BSPT / R) — Key Differences
| Feature | BSP Parallel (BSPP/G) | BSP Taper (BSPT/R) |
|---|---|---|
| Thread profile | Constant diameter | Tapers at 1:16 |
| Thread angle | 55° | 55° |
| Sealing method | Washer, O-ring or bonded seal | Metal-to-metal + PTFE tape/sealant |
| Standard | BS EN ISO 228-1 | BS 21 / BS EN 10226 |
| Designation | G (e.g., G 1/2) | R (male) / Rp (female parallel for taper male) |
| Common use | Hydraulics, instrumentation | Plumbing, gas, compressed air |
Common Plumbing Thread Combinations (UK)
- 1/2" BSP — Most common UK tap, valve, and fitting size. Basin taps, bath taps, radiator valves, flexible connectors.
- 3/4" BSP — Washing machine valves, outside taps, bath mixer feeds, larger radiator connections.
- 1" BSP — Main stopcock, gas meter connections, larger heating circuits.
- 1 1/4" and 1 1/2" BSP — Waste fittings (basin and bath traps), larger heating mains.
- 2" BSP — Larger commercial pipe connections, pumps.
Related Pages
See the UK Pipe Sizes reference and the UK Copper Pipe Sizes guide.
Frequently Asked Questions
Related Calculators
UK Copper Pipe Sizes
BS EN 1057 copper pipe sizes from 8–54 mm with outside diameters, wall thicknesses and working pressures.
UK Pipe Sizes
Standard UK plumbing and heating pipe sizes in copper, plastic and steel.
Skip Size Guide
Skip sizes from mini to RoRo with volume, weight limits and typical uses.
Drainage Pipe Sizes and Falls
Drainage pipe sizes and minimum fall gradients for foul and surface water.
Was this calculator helpful?
Last updated: April 2026
Verified against UK standards · estimates only, confirm with your supplier.