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Threaded Plumbing Fitting Identification Guide

Threaded Plumbing Fitting Identification Guide

How to identify AN, NPT and BSP plumbing fittings.

AN (JIC) 37° Flare 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.

Typical AN (JIC) 37° Male Fitting Profile
AN Size Thread Size
3AN 3/8 - 24
4AN 7/16 - 20
6AN 9/16 - 18
8AN 3/4 - 16
10AN 7/8 - 14
12AN 1 1/16 - 12
16AN 1 5/16 - 12
20AN 1 5/8 - 12
NPT Pipe Fittings (tapered thread)
(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.

Typical NPT Male Fitting Profile

Nominal Size Approx. Dia. at middle of taper Threads per inch
1/8 NPT 0.40 inch 27
1/4 NPT 0.53 inch 18
3/8 NPT 0.67 inch 18
1/2 NPT 0.83 inch 14
3/4 NPT 1.04 inch 14
1" NPT 1.30 inch 11 1/2
BSP Pipe Fittings (straight thread)
(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.

Typical BSP Male Fitting Profile
Nominal Size Thread Diameter Threads per inch
1/8 BSP 0.38 inch 28
1/4 BSP 0.51 inch 19
3/8 BSP 0.66 inch 19
1/2 BSP 0.81 inch 14
5/8 BSP 0.90 inch 14
3/4 BSP 1.04 inch 14
1 BSP 1.31 inch 11
High-Performance Plumbing - Major Product Category
AN Plumbing Adapters and Fittings
NPT Plumbing Adapters and Fittings
BSP Plumbing Adapters and Fittings
Thread Detective Thread Identifier Tools
Plumbing Technical Information

This article was first published on 12/4/2008.

It was most recently modified on 7/13/2022.