BSP Thread Sizes: BSPP and BSPT Dimensions & Identification
BSP (BSPP/BSPT) uses Parallel (BSPP) or tapered (BSPT) threads with a bonded washer or o-ring seal per BS 5200, ISO 228, ISO 7-1. Thread dimension table and identification tips below.
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
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.
Where BSP Falls Short
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 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.
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 Gets 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.
BSP (BSPP/BSPT): Common Questions
What is the difference between BSPP and BSPT?
BSPP (British Standard Pipe Parallel) has straight threads that do not seal on the thread. Sealing is done with a bonded washer or O-ring compressed against a flat face. BSPT (British Standard Pipe Taper) has tapered threads like NPT that seal by thread deformation, usually with sealant. Both use the same 55-degree Whitworth thread angle.
Can BSP connect to NPT?
No. BSP uses a 55-degree thread angle and NPT uses 60 degrees. The pitch (threads per inch) also differs at most sizes. At some sizes like 1/4 inch, the threads can partially engage, which is dangerous because it appears to fit but will fail under pressure. Always verify the thread standard with a gauge and use a proper BSP-to-NPT adapter. See the BSP vs NPT comparison for the full list of differences and how to tell them apart. Use the Adapter Finder to find the right adapter between BSP and NPT.
Where is BSP thread used?
BSP is the dominant pipe thread standard outside North America. It is used throughout Europe, the UK, Australia, the Middle East, and most of Asia. If you work on imported equipment from any of these regions, the hydraulic and pneumatic ports are almost certainly BSP, not NPT.
Reference data only. Verify thread dimensions with a thread identification gauge before making connections. Working with pressurized hydraulic systems involves serious injury risks including high-pressure injection, burns, and crushing hazards. This site does not replace manufacturer specifications, proper training, or employer safety procedures. See full terms of use.
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.