Nonmalleable (gray) cast iron articles go to 732510. Cast articles of malleable iron, ductile iron, or steel that are not specifically enumerated — such as grinding balls — fall under 732591 or 732599 depending on their form. The metallurgical designation on the mill certificate or technical specification is the primary evidence for the distinction.

Cast grinding balls are formed by casting and classify under 732591 within heading 7325. Forged or stamped grinding balls — produced by mechanical working — classify under heading 7326 (specifically 732611). The manufacturing process, documented by the producer, is the determining factor, and misclassification between the two headings is a common audit finding.