BSP (British Standard Pipe) is a widely adopted standard for plumbing connections across most of Europe. Unlike North America, where thread sizes are typically specified using distinct measurements, BSP threads are defined by the number of threads per inch (also known as "pitch") and the angle of the thread. BSP threads feature rounded peaks and valleys, following the Whitworth thread form.
There are two main types of BSP threads:
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BSPT – Tapered threads
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BSPP – Parallel threads
BSP sizes are always specified in imperial measurements. For example, our cast iron radiators are fitted with ½" BSP reducing bushes.
The table below provides a useful reference for standard BSP sizes, showing both metric (mm) and imperial (inch) equivalents.
| BSP Size | Actual Diameter |
|---|---|
| ⅛" | 0.35 inch, 9mm |
| ¼" | ½ inch, 12mm |
| ⅜" | 6/10 inch, 15mm |
| ½" | ¾ inch, 19mm |
| ¾" | 1 inch, 25mm |
| 1" | 1¼ inch, 31 mm |
| 1¼" | 1⅔ inch, 40 mm |
| 1½" | 1¾ inch, 45 mm |
| 2" | 2¼ inch, 57 mm |
| 2½" | 2 ⅞ inch, 73 mm |
| 3" | 3⅓ inch, 85 mm |
If you have any questions about your specific cast iron radiator installation, we recommend consulting your plumber or heating engineer for professional advice. Alternatively, feel free to contact our team on 01723 321 000 — we're always happy to discuss your requirements and help where we can.
