A bill of materials or engineering specification identifying the parent machine type, combined with a statement that the part does not fall under a more specific SITC or HTS heading, is the standard approach. Customs brokers often request OEM catalogs or technical drawings to confirm the residual classification is appropriate.

Mixed shipments should ideally be broken out by part type, since some components (e.g., parts for lifts or escalators) have their own dedicated headings. Where parts are genuinely interchangeable across machine types and no specific heading applies, the NES heading may cover the lot, but line-item detail on the commercial invoice reduces the risk of a customs query.