Single yarn (530610) consists of one strand spun from flax fibers. Multiple or cabled yarn (530620) is formed by twisting two or more single yarns together. The distinction matters because the two subheadings carry different duty rates and the construction affects downstream fabric performance.

Classification depends on the essential character rule and the fiber composition. If flax predominates by weight, the yarn may still fall under 5306; if cotton predominates, it would typically move to the cotton yarn chapters. Borderline blends require careful analysis of the Section XI notes and, where uncertain, a binding ruling from CBP.