Customs authorities generally require that the part be designed and marketed for use across the relevant machine categories — not merely that it is physically interchangeable. Technical specifications, product literature, and sales documentation showing cross-category application are the most persuasive evidence. Parts designed for a single machine type should be classified with that machine's parts heading instead.

Section 301 applicability is determined at the HTS subheading level, and the rate or coverage for multi-use parts may differ from that of parts classified under a specific machine heading. Importers should verify the current Section 301 status of the applicable HTS subheading — not just the SITC code — before entry, as coverage has been updated through multiple rounds of product exclusions and reinstatements.