What is difference between NPS and OD of a pipe?

NPS : Mean Nominal Pipe Size, it is American standard  set of standard sizes for pipes used for high or low pressures and temperatures

OD : Mean Outside Diameter

NPS- nominal pipe size 

OD-outside diameter 

NPS - nominal pipe inch size (nomally used simbol ")

OD - outside diameter 

NPS : Mean Nominal Pipe Size.

OD : Mean Outside Diameter.

NPS - nominal pipe inch size 

OD - outside diameter

In fact, NPS is used more than the actual size of the tube as a way to distinguish tubes from each other and name them.

But the OD in the pipe means the outer diameter of the pipe.

Nominal Pipe Size :   for diameter based on inches, and a schedule (Sched. or Sch.) for wall thickness. NPS is often incorrectly called National Pipe Size, due to confusion with national pipe thread (NPT)

NPS is the size of the of the internal diameter of the pipe and OD is the outside diameter of the pipe.

NPS : IS NOMINAL SIZE OF PIPE IN  AMEROCAN STANDARDS  (INCH SIZES)AND THEY ARE STANDARD VALUES LIKE STEPS OF PIPE SIZES   , OD : IS OUTSIDE DIAMETER OF PIPE  THUS TWO VALUES ARE CONSTANT ACCORDORING TO STANDARDS . NOTE THE SAME SIZE OF NPS HAS SEVERAL SCHDULES  THAT WILL CHANGE WALL THICKNESS AND INTERNAL DIAMETER ACCORDING TO PRESSURE USES 

 Mean Nominal Pipe Size.

nominal pipe inch size (nomally used simbol 

NPS : Mean Nominal Pipe Size.

OD : Mean Outside Diameter.