BSP Thread Size Converter
Convert BSP pipe thread sizes into actual outside diameter, millimeters, threads per inch, and metric pitch for BSPP parallel and BSPT tapered fittings.
Convert a BSP thread size
Pick the BSP size stamped on a fitting, or enter a measured male thread outside diameter to find the closest nominal size.
Choose a BSP size or enter a measured OD.
BSP thread size chart
Use this quick chart to compare nominal BSP sizes with approximate male thread major diameters and thread pitch.
| BSP size | Major OD inches | Major OD mm | TPI | Pitch mm |
|---|
How to use this BSP converter
- Select the nominal BSP size to see its common reference dimensions.
- If you have a fitting in hand, measure the outside of the male threads with calipers.
- Enter the measurement to see the closest BSP size and the difference from the chart value.
BSP sizes are nominal pipe thread names. The size name is not the actual outside diameter, so a 1/2 BSP male thread measures about 0.825 inches, not 0.500 inches.
BSPP, BSPT, and NPT notes
- BSPP / G: parallel thread, often seals with a washer, bonded seal, or O-ring face.
- BSPT / R: tapered thread, commonly used where the thread form helps make the seal.
- NPT: uses a different 60° thread form. BSP uses a 55° Whitworth form, so adapters should be chosen deliberately.
For hydraulic, air, water, gas, or pressure work, confirm the fitting standard, sealing method, material, and pressure rating before assembly.
BSP converter FAQ
What is 1/2 BSP in inches and millimeters?
1/2 BSP has an approximate male thread major outside diameter of 0.825 inches, or 20.96 millimeters, with 14 threads per inch.
How do I identify a BSP thread?
Measure the male thread outside diameter and count the threads per inch. Compare both values to a BSP chart, then confirm whether the fitting is BSPP parallel or BSPT tapered.
Can BSP and NPT fittings be mixed?
They should not be treated as direct substitutes. Some nominal sizes are close in outside diameter, but the thread angle, pitch, taper, and sealing style can differ.