Understanding BSP Thread Sizes
BSP (British Standard Pipe) thread sizes are the recognised standard across the plumbing and sanitary industry. Used worldwide, this measurement system ensures compatibility for fittings, valves and tap connections in both domestic and commercial applications.
If you’re unsure which size you have, this quick guide will help you identify the correct BSP thread so you can find the right replacement part with confidence.
Common BSP Sizes
3/8″, 1/2″, 3/4″, 1″, 1.25″, 1.5″
Measuring BSP Sizes
| BSP Size | Diameter of Thread (mm) | Typical Applications |
|---|---|---|
| 3/8" | 15.6mm | Small caravan taps, European-size flexi-tail connectors |
| 1/2" | 20.9mm | Shower hoses, basin tap valves, UK flexi-tail connectors |
| 3/4" | 26.4mm | Bath tap tails, bath mixer valves |
| 1" | 33.2mm | Basin waste fittings |
| 1.25" | 41.9mm | Larger basin or bath waste fittings |
| 1.5" | 47.8mm | Bath and sink waste outlets |
Example
If you have a 3/4″ quarter-turn ceramic disc tap valve, the 3/4″ refers to the thread size on the cartridge that screws into your tap. When measured across the thread, it will be approximately 26.4mm in diameter.
Tap Aerator & Nozzle Measurements
To find the correct aerator or nozzle for your tap, compare your existing fitting to the sizes below. These measurements are approximate and should be used as a guide only.
| Type | Size | Diameter A (mm) | Diameter B (mm) |
|---|---|---|---|
| Male | M18 | 17.9 | 16.4 |
| Male | M20 | 19.6 | 18.3 |
| Male | M24 | 23.5 | 22.0 |
| Male | M28 | 27.5 | 25.6 |
| Female | F22 | 23.5 | 21.5 |
Need Help Identifying Your Size?
Our experts at Hart Plumbing Spares are here to help. Whether you’re replacing a tap valve, waste fitting or flexi-tail connector, we’ll make sure you get the right size and part – first time.
