Start with the heading that describes the complete machine or apparatus the part belongs to — many headings explicitly include 'parts thereof.' If the part is described by its own specific heading (e.g., a switch, relay, or connector), it classifies there regardless of what machine it serves. Only after exhausting those options, and confirming the part is not covered by any other heading in the chapter or in Section XVI's general parts notes, does 8548 apply.

Yes. A shipment of mixed electrical parts should be classified line by line: each distinct article goes to its most specific applicable heading. Bundling everything under 8548 for convenience is incorrect and can trigger CBP scrutiny. Where a part's classification is genuinely uncertain, a binding ruling request provides certainty before importation.