How to identify AN, NPT and BSP plumbing fittings.
(same thread used on SAE O-ring ports)
AN Plumbing Fittings have SAE UNF (parallel) threads. Male AN fittings have a 37° convex flare where the fitting seals. O-ring boss adapters use the same thread sizes, but have no seat. They seal at the port face.
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(American Standard Pipe)
NPT Fittings have tapered (conical) threads and seal by an interference fit at the threads. They require a thread sealant.
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(British Standard Pipe)
BSP Fittings have straight (parallel) threads. They seal either by a 30° concave flare on the male fitting, or at the port face. Port face sealing requires an O-ring or sealing washer.
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