What do all pipe classes with the same nominal pipe size have in common?

The correct answer focuses on the standardization of nominal pipe sizes in piping systems. All pipe classes with the same nominal pipe size are designed to have the same inside diameter. This standardization is crucial because it allows various pipes and fittings to be interconnected within a system reliably.

While different classes of pipes may vary in their wall thickness, weight, and length, the nominal size is a designation that primarily pertains to the inside diameter. This means that regardless of whether a pipe is made from different materials or has different pressure ratings, if it carries the same nominal size designation, its inside diameter will remain consistent across the board. This is essential for ensuring proper fluid flow and compatibility when connecting piping materials of different classes in installations managing fluids or gases.