BSPP / BSPT THREAD IDENTIFICATION GUIDE
British Standard Pipe Parallel / British Standard Pipe Taper
55° Whitworth Thread Form Technical Guide
What is BSP Thread?
BSP (British Standard Pipe) thread is one of the most commonly used thread forms
for hydraulic fittings, pneumatic systems, valves, adapters, instrumentation fittings
and industrial pipe connections.
BSP threads use a 55 Degree thread angle and are available in two major forms:
- BSPP (G Thread) — Parallel Thread
- BSPT (R Thread) — Taper Thread
BSPP vs BSPT Difference
| Feature | BSPP | BSPT |
|---|---|---|
| Thread Type | Parallel | Tapered |
| Designation | G | R |
| Sealing Method | O-Ring / Washer / Bonded Seal | Thread Interference |
| Thread Diameter | Constant | Reduces Along Length |
| Applications | Ports, Adaptors, Hydraulic Fittings | Pipe Connections, Plumbing, Gas Lines |
How to Identify BSP Threads
Step 1 — Measure Outside Diameter (Major Diameter)
Use vernier caliper to measure thread OD.
Step 2 — Count Threads Per Inch (TPI)
Use thread gauge and compare pitch.
Step 3 — Check Thread Profile
BSP threads have 55° Whitworth form.
Step 4 — Check if Parallel or Taper
• Same diameter along length = BSPP
• Reducing diameter = BSPT
BSP Thread Dimension Chart
| Size | TPI | Major (Ext) | Minor (Int) | Tap Drill |
|---|---|---|---|---|
| 1/8″ | 28 | 9.728 | 8.566 | 8.70 |
| 1/4″ | 19 | 13.157 | 11.445 | 11.60 |
| 3/8″ | 19 | 16.662 | 14.950 | 15.00 |
| 1/2″ | 14 | 20.955 | 18.631 | 19.00 |
| 5/8″ | 14 | 22.911 | 20.587 | 20.75 |
| 3/4″ | 14 | 26.441 | 24.117 | 24.50 |
| 7/8″ | 14 | 30.201 | 27.877 | 28.00 |
| 1″ | 11 | 33.249 | 31.770 | 30.50 |
| 1-1/4″ | 11 | 41.910 | 38.952 | 39.50 |
| 1-1/2″ | 11 | 47.803 | 44.845 | 45.00 |
| 2″ | 11 | 59.614 | 56.656 | 57.00 |
| 3″ | 11 | 87.884 | 84.926 | 85.50 |
| 4″ | 11 | 113.030 | 110.072 | 110.50 |
Common BSP Applications
- Hydraulic Adaptors
- Instrumentation Tube Fittings
- Needle Valves
- Pressure Gauges
- Ball Valves
- Pneumatic Connectors
- Pipe Fittings and Couplings
Common Identification Errors
Avoid confusing:
- BSP with NPT (Different Thread Angle — NPT is 60°)
- BSPP with BSPT (Parallel vs Taper)
- Nominal Pipe Size with Actual Thread Diameter
BSP vs NPT Comparison
| Feature | BSP | NPT |
|---|---|---|
| Thread Angle | 55° | 60° |
| Crest / Root | Rounded | Sharp |
| Interchangeable | No | No |
Ordering Guide
When ordering BSP threaded components, always specify:
- Thread Type (BSPP or BSPT)
- Size (Example 1/2″)
- Male or Female
- Material (SS304 / SS316 / Brass / Carbon Steel)
- Pressure Rating
- Seal Type (if BSPP)
Example Product Designation
1/2″ BSPP Male x 12mm Tube Connector SS316
1/4″ BSPT Male Needle Valve 6000 PSI SS304
Technical Note
G = BSPP Thread
R = BSPT Thread
BSP threads follow Whitworth thread form and are governed by applicable British standards.
Always verify fitment before installation.
