BSP Thread Sizes: BSPP and BSPT Dimensions & Identification
BSP (BSPP/BSPT) Thread Sizes
| Nominal Size | Threads/Inch | OD |
|---|---|---|
| 1/8" | 28 TPI | 0.383" |
| 1/4" | 19 TPI | 0.518" |
| 3/8" | 19 TPI | 0.656" |
| 1/2" | 14 TPI | 0.825" |
| 3/4" | 14 TPI | 1.041" |
| 1" | 11 TPI | 1.309" |
| 1-1/4" | 11 TPI | 1.650" |
| 1-1/2" | 11 TPI | 1.882" |
| 2" | 11 TPI | 2.347" |
BSP is the international metric-world counterpart to NPT. It comes in two variants: BSPP (parallel, straight threads) which seals with a bonded washer or O-ring, and BSPT (tapered) which seals by thread interference like NPT. The thread angle is 55 degrees (Whitworth), not 60 degrees like NPT, so they are NOT interchangeable even when sizes look similar. This is the most common thread mix-up in hydraulics.
When to Use BSP (BSPP/BSPT)
European and Asian hydraulic equipment, marine systems, and global industrial machinery.
If the equipment was built outside North America, check for BSP before assuming NPT.
BSPP with a bonded seal is a reliable, reusable connection.
BSP (BSPP/BSPT) Limitations
Easily confused with NPT. The 55-degree vs 60-degree thread angle difference is hard to see without a gauge, but cross-threading BSP into NPT ports causes leaks and thread damage.
Always verify with a thread ID gauge.
How to Identify BSP (BSPP/BSPT) Fittings
Measure the thread angle with a gauge. BSP is 55 degrees, NPT is 60 degrees. BSP threads are often marked with G (parallel) or R (tapered) prefix.
BSP (BSPP/BSPT) Measurement Tips
The critical distinction is between BSPP (parallel/straight) and BSPT (tapered). BSPP uses a bonded seal or dowty washer to create the seal on a flat face. BSPT seals by thread taper, similar to NPT. If you see a BSP fitting on European or Asian equipment, check whether it is parallel or tapered before ordering a replacement. Using the wrong type will either leak or not thread in.
What BSP (BSPP/BSPT) Is Confused With
BSP and NPT look similar but are NOT interchangeable. The thread angle is different (55 degrees for BSP vs 60 degrees for NPT) and the pitch is different at most sizes. A 1/2 inch BSP fitting has 14 threads per inch while a 1/2 inch NPT has 14 as well, but the thread form prevents a proper seal. Cross-threading BSP into NPT ports is a common cause of hydraulic leaks on imported equipment.
Data sourced from BS 5200, ISO 228-1, ISO 7-1. Thread dimensions are nominal values. Always verify with a thread identification gauge before making connections.