Which designation is used to indicate pipe size in metric units?

• A. Metric nominal size
• B. Imperial nominal size
• C. Nominal wall thickness
• D. Outer diameter

Answer: (A)

In metric piping, the size is indicated by a metric nominal size. This labeling provides a standard reference for the pipe’s intended bore and compatibility across fittings and components, independent of the exact wall thickness or outer diameter. The imperial nominal size is for inches, so it doesn’t apply to metric systems. Nominal wall thickness describes how thick the pipe is, not the size label, and outer diameter is a physical dimension, not the standardized size designation used in metric piping.