BSP vs NPT: Thread Angle Differences & Global Fitting Standards
BSP (British Standard Pipe) and NPT (National Pipe Thread) are the two dominant pipe thread standards worldwide. BSP uses a 55-degree thread angle; NPT uses...
Key Differences
BSP has a 55-degree thread angle (Whitworth form).
NPT has a 60-degree thread angle (American National form).
BSP comes in two variants: BSPP (parallel/straight) and BSPT (tapered).
NPT is always tapered.
The pitch (threads per inch) differs at most sizes.
BSP dominates outside North America; NPT dominates inside North America.
When to Choose BSP (BSPP/BSPT)
Equipment manufactured to European, UK, Australian, or Asian specifications
Existing systems already using BSP
International hydraulic equipment
Metric-based installations.
When to Choose NPT
North American hydraulic and pneumatic systems
Equipment manufactured to US specifications
Plumbing and HVAC in North America
When sourcing from US suppliers.
Practical Notes
The threads look identical to the eye but the angle difference means they will cross-thread and leak. At some sizes (like 1/4 inch), BSP and NPT threads can partially engage, which is dangerous because it appears to fit but will fail under pressure. Always verify the thread standard before connecting.
Common Mistake
Importing European equipment and connecting it to NPT shop air or hydraulic lines. The ports are BSP and need adapters or replacement fittings to connect to NPT systems.