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BSP/USA pipe O.D. (outside diameter)
comparison chart

Be careful when specifying Nominal Pipe Sizes. They could either be USA sizes, or BSP (British Standard Pipe) sizes which are similar to but NOT the same. Generally, when a thread specification is called out on a pipe, it will determine which system is needed. However, this is not an absolute. Many of the pipe sizes will support either the BSP or USA (NPT) threads.

Nominal
Pipe
Size
BSP
pipe
O.D. in mm
BSP
pipe
O.D. in inches
USA
pipe
O.D. in mm
USA
pipe
O.D. in inches
1/8 10.2 0.402 10.3 0.405
1/4 13.5 0.531 13.7 0.540
3/8 17.2 0.677 17.1 0.675
1/2 21.3 0.839 21.3 0.840
3/4 26.9 1.059 26.7 1.050
1 33.7 1.327 33.4 1.315
1 1/4 42.4 1.669 42.2 1.660
1 1/2 48.3 1.902 48.3 1.900
2 60.3 2.375 60.3 2.375
2 1/2 76.1 2.996 73 2.875
3 88.9 3.500 88.9 3.500
3 1/2 101.6 4.000 101.6 4.000
4 114.3 4.500 114.3 4.500
5 139.7 5.500 141.3 5.563
6 165.1** 6.500 168.3 6.625
8 219.1 8.626 219.1 8.625
10 273 10.75 273 10.75
12 323.9 12.75 323.8 12.75
14 355.6 14.000 355.6 14.000
16 406.4 16.000 406.4 16.000
18 457 17.992 457.2 18.000
20 508 20.000 508 20.000
**Depending upon the standard number, this may also be 168.3 mm

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