Specifies the nominal pipe diameter (NPD) to use for this pipe run. The pipe specification controls the available NPDs in this list. If you select an equipment nozzle as the starting point of your pipe run, the software automatically uses the NPD of the nozzle as the NPD of the pipe run. You can select the NPD units to display on a session file basis using the Menu > Options Command on the Units of Measure Tab (Options Dialog).