Not a direct fit. Joining 3" NPT (National Pipe Taper) to 3" BSP tapered (R3 / BSPT) needs a 3 NPT to R3 BSP tapered adapter. Sealing method, the real-world trap, and the exact adapter to buy.

Updated 05 September 2026.

HoseFitFinder / Every thread and fitting standard

Connect 3" NPT (National Pipe Taper) to 3" BSP tapered (R3 / BSPT)

How to join 3-8 NPT and R3, and what stops it leaking.

Needs adapter
End A
3" NPT (National Pipe Taper) (3-8 NPT)
Seals on on the thread flanks with PTFE tape
via adapter
End B
3" BSP tapered (R3 / BSPT) (R3)
Seals on on the thread flanks with PTFE tape or paste
Adapter needed3 NPT to R3 BSP tapered adapter

Not a direct fit. Joining 3" NPT (National Pipe Taper) to 3" BSP tapered (R3 / BSPT) needs a 3 NPT to R3 BSP tapered adapter.

The adapter to buy

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3 NPT and R3 BSPT are both tapered 3 inch threads, which fools people into forcing them together, but the flank angle differs: 60 degree on NPT, 55 degree on BSPT. They cannot seal against each other, so an NPT-to-BSP-tapered adapter is the correct fix.

Both being tapered at 3 inch is the trap. Same taper, wrong flank angle: the joint starts smoothly then leaks. Use the adapter, not extra tape.

Related connections

3" NPT (National Pipe Taper)3-8 NPT3" BSP tapered (R3 / BSPT)R33" BSP parallel (G3 / BSPP) to 3" BSP tapered (R3 / BSPT)adapter3" NPT (National Pipe Taper) to 3" BSP parallel (G3 / BSPP)adapter3" NPSH straight hose thread to 3" NPT (National Pipe Taper)adapter3" NH fire hose thread (NST) to 3" NPT (National Pipe Taper)adapter

Questions and answers

Connect 3" NPT (National Pipe Taper) to 3" BSP tapered (R3 / BSPT)?

Not a direct fit. Joining 3" NPT (National Pipe Taper) to 3" BSP tapered (R3 / BSPT) needs a 3 NPT to R3 BSP tapered adapter.