Amazing Value
Quality Products, Best Prices. Australian Owned & Operated
BSW Thread Pitch Chart
The BSW Thread Chart is an essential reference tool for engineers, machinists, maintenance technicians, apprentices and workshop professionals who work with British Standard Whitworth threads. Whether you're restoring vintage machinery, servicing classic British vehicles or maintaining older industrial equipment, this quick reference guide provides the thread sizes and tap drill specifications you need.
| Diameter | TPI | Drill Size (mm) |
|---|---|---|
| 1/8" | 40 | 2.5 mm |
| 5/32" | 32 | 3.1 mm |
| 3/16" | 24 | 3.7 mm |
| 1/4" | 20 | 5.1 mm |
| 5/16" | 18 | 6.5 mm |
| 3/8" | 16 | 7.9 mm |
| 7/16" | 14 | 9.3 mm |
| 1/2" | 12 | 10.5 mm |
| 9/16" | 12 | 12.0 mm |
| 5/8" | 11 | 13.5 mm |
| 11/16" | 11 | 15.0 mm |
| 3/4" | 10 | 16.5 mm |
| 7/8" | 9 | 19.25 mm |
| 1" | 8 | 22.0 mm |
| 1-1/8" | 7 | 24.75 mm |
| 1-1/4" | 7 | 28.0 mm |
| 1-1/2" | 6 | 34.0 mm |
| 1-3/4" | 5 | 39.5 mm |
| 2" | 4.5 | 45.0 mm |
| 2-1/4" | 4 | 50.5 mm |
| 2-1/2" | 4 | 57.0 mm |
What is a BSW Thread?
BSW stands for British Standard Whitworth, a thread standard developed by Sir Joseph Whitworth in the 19th century. BSW threads feature a distinctive 55° thread angle and were the dominant fastening standard in Britain and the Commonwealth for decades.
Although metric threads are now more common in modern manufacturing, Whitworth threads remain widely used in:
- Vintage machinery and equipment
- Classic British cars and motorcycles
- Agricultural and heritage equipment
- Restoration and conservation projects
- Older industrial installations
Understanding BSW thread dimensions is crucial for anyone working with pre-metric British engineering.
How to Read the BSW Thread Chart
The chart above displays the key specifications for common Whitworth thread sizes:
- Diameter – The nominal thread size in imperial measurements (1/8" through 2-1/2")
- TPI – Threads Per Inch, indicating how many threads fit within one inch of length
- Drill Size (mm) – The recommended tap drill diameter in millimetres for creating the threaded hole
Use the tap drill size when preparing holes for BSW taps to ensure proper thread engagement and avoid damage to your tools or workpiece.
Common Applications
BSW thread reference charts are indispensable in several industries and settings:
- Engineering workshops – For precision machining and custom fabrication
- Maintenance and repair – Replacing fasteners in older equipment
- Restoration projects – Ensuring authenticity when rebuilding vintage machinery
- Classic vehicle servicing – British motorcycles and cars often use BSW fasteners
- Agricultural equipment – Many heritage farm machines rely on Whitworth threads
Frequently Asked Questions
What does BSW stand for?
BSW stands for British Standard Whitworth, a thread standard developed in the 1800s and widely used throughout the British Commonwealth.
What is the difference between BSW and BSF?
BSW (British Standard Whitworth) and BSF (British Standard Fine) are both imperial thread standards. BSF threads have a finer pitch (more threads per inch) than BSW, making them suitable for applications requiring greater precision or where space is limited.
Are BSW threads metric?
No. BSW threads use imperial measurements (inches and fractions of inches). However, the tap drill sizes are often expressed in millimetres for convenience, as shown in the chart above.
Are BSW threads still used today?
Yes. While metric threads dominate modern manufacturing, BSW threads remain essential for maintaining, repairing and restoring vintage machinery, classic vehicles and heritage equipment. Any workshop dealing with pre-1970s British engineering will encounter Whitworth threads regularly.