What is the approximate difference in size between the outside diameter of schedule 40 black iron pipe and its nominal size?

The correct choice highlights that there is a consistent and well-defined relationship between the nominal size and the actual outside diameter of schedule 40 black iron pipe. The nominal size refers to a standardized designation that conveys the approximate internal diameter of the pipe, while the actual outside diameter is larger due to the thickness of the pipe walls.

For schedule 40 black iron pipe, the difference typically reflects a 1/4 inch increment. For instance, a nominal size of 1 inch correlates to an outside diameter of approximately 1.315 inches. This consistent relationship is important in plumbing and pipefitting applications because it ensures compatibility with fittings and fixtures designed for those nominal sizes.

Understanding this difference helps professionals select the correct materials and avoid miscalculations in projects involving piping systems. Consequently, being aware that the outside diameter is approximately 1/4 inch larger than the nominal size is essential for proper installation and application of black iron pipe.