DIFFERENCE OF DN OD NPS NB – OUTER DIAMETER AND NOMINAL DIAMETER OF PIPE
DN means the nominal diameter of pipe, that is the average of outer diameter and inner diameter. OD means the outside diameter of pipe. For instance, DN50 pipe means 2″ and the outside diameter is 60.33mm.

PIPE SIZE INFORMATION LIST
Pipe Size，North America call it NPS，expressed in inch sizes. Europe call it DN，expressed in Metric sizes.
OD means Outside Diameter， SCH means different size pipe’s wall thickness. (You will find different size pipes under same SCH, the wall thickness is different.)