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Connect 1/4" NPT (National Pipe Taper) to 1/4" BSP parallel (G1/4 / BSPP)

How to join 1/4-18 NPT and G1/4, and what stops it leaking.

Needs adapter

End A

1/4" NPT (National Pipe Taper) (1/4-18 NPT)

Seals on on the thread flanks with PTFE tape

via adapter

End B

1/4" BSP parallel (G1/4 / BSPP) (G1/4)

Seals on flat washer or bonded seal on the face

Adapter needed1/4 NPT to 1/4 BSP adapter

Not a direct fit. Joining 1/4" NPT (National Pipe Taper) to 1/4" BSP parallel (G1/4 / BSPP) needs a 1/4 NPT to 1/4 BSP adapter.

The adapter to buy

Search Amazon for 1/4 NPT to 1/4 BSP adapteraffiliate search Find 1/4 NPT to 1/4 BSP adapter on eBayaffiliate

1/4 NPT and G1/4 are the classic air-line mismatch: both common, both 1/4 inch, neither compatible. NPT is 60 degree tapered, BSP is 55 degree. A 1/4 NPT-to-BSP adapter joins US and European air tools reliably.

This bites people importing US air tools into the UK. The fitting screws in far enough to feel right, then blows off under pressure. Use the adapter, not tape.

Related connections

1/4" NPT (National Pipe Taper)1/4-18 NPT 1/4" BSP parallel (G1/4 / BSPP)G1/4

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