Tubes and pipes have a circular cross-section and are designed primarily to convey fluids or gases. Hollow profiles may have any non-circular cross-section (square, rectangular, oval, or complex shapes) and are classified under the bars, rods, and profiles heading. When a circular hollow section is clearly structural rather than fluid-conveying, the intended use and cross-sectional shape together guide the classification decision.

A producer's mill certificate specifying the alloy designation is the standard document. Unalloyed aluminum (1xxx series) and alloy grades (2xxx through 8xxx series) are treated differently under the heading, and CBP may request chemical composition data during examination or a post-entry audit to verify the declared subheading.