Nominal Pipe Size (NPS)

The term used as a guideline number defining the diameter
of the pipe. Nominal pipe size refers to only the outside diameter (OD) of a pipe.

Nominal Bore (NB)

The European designation equivalent to NPS, in which sizes are measured in millimetres. NB (nominal bore) is also frequently used interchangeably with NPS.   

Diameter Nominal (DN) 

The international and European metric method used to describe NPS (or NB).
DN pipe sizes numbers are therefore different to NPS.

Outside Diameter (OD)

OD is the outside diameter of the pipe and is fixed for a given size. The NPS is related to the inside diameter
in inches

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