"Parts" classification is one of the most contested areas of customs law. Under Additional U.S. Rule 1(c), a specific eo nomine provision generally prevails over a "parts of" provision — but this is only one of many layers.
CBP and the courts apply two main tests for parts classification:
- Bauerhin Test — A part must be "an integral, constituent or component part, without which the article to which it is to be joined could not function as such article."
- Pompeo Test — A part must be a part of a particular article, dedicated solely or principally for use with that article.
Even if an article qualifies as a "part," classification depends on the structure of the relevant heading or chapter. Many chapters have specific notes excluding parts from particular headings — for example, Section XVI Note 2 provides detailed rules for parts of machinery in Chapters 84 and 85.
Common parts disputes involve:
- Multi-use parts that fit several finished articles
- Parts that are themselves provided for eo nomine in another heading
- Articles that could be either "parts" or "accessories"