Which statement correctly describes the relationship between CT pipe outer diameter and callout size?

• A. A CT pipe with an OD of 1 1/8 inches has a callout of 1 inch.
• B. A CT pipe with an OD of 1 1/8 inches has a callout of 2 inches.
• C. A CT pipe with an OD of 1 1/8 inches has a callout of 1/2 inch.
• D. A CT pipe with an OD of 1 1/8 inches has a callout of 1 1/4 inch.

Answer: (A)

In copper tube sizing, the callout (nominal size) is not the same as the actual outside diameter. The nominal size is a rough reference used for fittings and represents the approximate inner diameter, while the outside diameter follows a standard table. For a 1 inch nominal copper tube, the outside diameter is 1-1/8 inches. So an outer diameter of 1-1/8" corresponds to a callout of 1 inch. This relationship is why that statement is correct: the OD aligns with the standard copper-tube sizing where 1-1/8" OD maps to a 1" nominal size.