BSP Thread to MM Calculator
Technical Reference for Heater Flanges & Fittings
Actual OD (Approx)
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Threads Per Inch (TPI)
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BSP Thread Reference Chart
| BSP Size | Major OD (mm) | TPI (Pitch) | Typical Use |
|---|---|---|---|
| 1/4″ BSP | 13.16 mm | 19 | Small probes |
| 1/2″ BSP | 20.95 mm | 14 | Common immersion heaters |
| 1″ BSP | 33.25 mm | 11 | Industrial water heaters |
| 1.25″ BSP | 41.91 mm | 11 | Standard boiler elements |
| 1.5″ BSP | 47.80 mm | 11 | Heavy duty immersion |
| 2″ BSP | 59.61 mm | 11 | Large flange assemblies |
Note: BSP (British Standard Pipe) sizes refer to the nominal internal diameter of the pipe, not the actual thread diameter. Always measure the OD of your existing thread before ordering to ensure a perfect fit with Wilson Heat flanges.