Connect 1/2" NPT (National Pipe Taper) to 1/2" BSP parallel (G1/2 / BSPP)
How to join 1/2-14 NPT and G1/2, and what stops it leaking.
Needs adapter
End A
1/2" NPT (National Pipe Taper) (1/2-14 NPT)
Seals on on the thread flanks with PTFE tape
via adapter
End B
1/2" BSP parallel (G1/2 / BSPP) (G1/2)
Seals on flat washer
Adapter needed1/2 NPT to 1/2 BSP adapter
Not a direct fit. Joining 1/2" NPT (National Pipe Taper) to 1/2" BSP parallel (G1/2 / BSPP) needs a 1/2 NPT to 1/2 BSP adapter.
The adapter to buy
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1/2 NPT and G1/2 both run 14 TPI, which fools people into forcing them together. The 60 versus 55 degree flank angle still means they cannot seal. A 1/2 NPT-to-BSP adapter is the correct fix.
The matching 14 TPI is a trap. Same pitch, wrong flank angle. It will start smoothly then leak; do not rely on tape to close the gap.
Related connections
1/2" NPT (National Pipe Taper)1/2-14 NPT1/2" BSP parallel (G1/2 / BSPP)G1/2Garden Hose Thread (GHT / NH) to 1/2" BSP parallel (G1/2 / BSPP)adapter1/2" BSP parallel (G1/2 / BSPP) to 3/4" BSP parallel (G3/4 / BSPP)adapter3/8" BSP parallel (G3/8 / BSPP) to 1/2" BSP parallel (G1/2 / BSPP)adapter1-1/2" NH fire hose thread (NST) to 1/2" NPT (National Pipe Taper)adapter
Sources: ANSI/ASME B1.20.1 (NPT pipe threads) · NPT thread dimensions chart (ASME B1.20.1), Machining Doctor · ISO 228-1 (G / BSPP parallel pipe threads) · BSP thread dimensions chart (ISO 228 / ISO 7), AmesWeb