Which measurement describes the inside dimension of the pipe covering when given as 3 inches by 1/2 inch?

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

Answer: (A)

When a pipe covering is described as inside diameter by wall thickness, the first number tells you the space inside the pipe, while the second number tells you how thick the wall around that space is. So 3 inches by 1/2 inch means the interior opening is 3 inches across, and the wall thickness is 1/2 inch. Therefore the inside dimension is 3 inches. The 1/2 inch is not the interior size but the thickness; if you wanted the outside diameter, you’d add twice the thickness to the inside diameter (3 + 2 × 1/2 = 4 inches).