Threaded Plumbing Fitting Identification Guide
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.
Click here for more Technical Information About AN Plumbing Fittings and Hose.
(American Standard Pipe)
NPT Fittings have tapered (conical) threads and seal by an interference fit at the threads. They require a thread sealant.
Click here for more Technical Information About NPT Plumbing Fittings.
(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.
Click here for more Technical Information about BSP Plumbing Fittings.
This article was first published on 12/4/2008.
It was most recently modified on 3/25/2015.