If a CT pipe has an outer diameter of 1 1/8 inches, what is its callout size?

• A. 1/2 inch
• B. 1/4 inch
• C. 3/4 inch
• D. 1 inch

Answer: (D)

In copper tube sizing the callout (nominal) size is not the same as the exact outside diameter. The standard outer diameters map to nominal sizes, so a 1-inch nominal tube has an outer diameter of 1 1/8 inches. Therefore, with an outer diameter of 1 1/8 inches, the callout size is 1 inch. Other nominal sizes would have smaller outer diameters (for example, a 1/2 inch nominal tube isn’t 1/2 inch OD but 5/8 inch, and a 3/4 inch nominal tube is 7/8 inch OD).