"Michael Koblic" wrote in message
...

"RoyJ" wrote in message
m...
Pipe sizes were defined in the 'old days' when everything was threaded
connections and you needed to be able to flow a certain amount of gas or
liquid.

Pipe has a defined OD so all the different pipe fittings can be be
attached. The ID is sized so that "normal" wall thickness (designated
'Schedule 40')will give an ID that is equal to or larger than the nominal
dimension. After that, there are Schedule 5, 10, 20, 40, 80, and 160 to
handle different pressures which give you all the different wall
thicknesses. Confused yet?


OK, if I understand you right the nominal size refers to the ID but it is
the *OD* that is held constant and the ID varies with the schedule and the
wall thickness. Why, that makes perfect sense!

Not surprising I feel like Alice in wonderland...

You got it!!

Don Young