Not a direct fit. Joining 1" NPT (National Pipe Taper) to 1" BSP parallel (G1 / BSPP) needs a 1 NPT to G1 BSP adapter. Sealing method, the real-world trap, and the exact adapter to buy.
Updated 05 September 2026.
Connect 1" NPT (National Pipe Taper) to 1" BSP parallel (G1 / BSPP)
How to join 1-11.5 NPT and G1, and what stops it leaking.
Not a direct fit. Joining 1" NPT (National Pipe Taper) to 1" BSP parallel (G1 / BSPP) needs a 1 NPT to G1 BSP adapter.
The adapter to buy
1 NPT and G1 BSP are both called 1 inch but do not interchange: NPT is a 60 degree thread form and BSP is 55 degree, so they engage a turn or two then jam without sealing. A machined NPT-to-BSP adapter is required; PTFE tape alone cannot fix the thread-form mismatch.
At 1 inch the two look close enough to force together. The 60 versus 55 degree flank angle means the threads never fully mate, so add the correct adapter rather than more tape.
Related connections
Questions and answers
Connect 1" NPT (National Pipe Taper) to 1" BSP parallel (G1 / BSPP)?
Not a direct fit. Joining 1" NPT (National Pipe Taper) to 1" BSP parallel (G1 / BSPP) needs a 1 NPT to G1 BSP adapter.