The classification process requires first checking whether the part is specifically described in any other horological heading — for example, movements, cases, or straps each have dedicated headings. Only parts that are not more specifically provided for elsewhere should be classified here. A detailed technical description and, where possible, a ruling from customs authorities can prevent misclassification.

Jewels used as bearings in watch movements and mainsprings are generally considered watch parts and can fall within this residual heading when not more specifically classified elsewhere. However, unworked jewels may classify under gem or mineral headings depending on their state of manufacture, so the degree of processing and the commercial purpose of the article are both relevant to the final classification determination.