Parts imported separately from complete frames — such as bulk shipments of hinges, temples, or nose pads — are classified under 900390. However, when parts are imported together with complete frames as a set or kit, GRI 3 (sets) or the essential character rule may require classification of the entire shipment under the frame heading. The presentation and commercial packaging at the time of importation are key factors, and importers should avoid commingling bulk parts with finished frames in the same shipment without clear documentation.

Mexico's leading position under this heading largely reflects its role in regional eyewear assembly and finishing, where US-bound frame components — including those originally manufactured in China, Italy, or Taiwan — are processed or kitted before final import. USMCA rules of origin govern whether such goods qualify for preferential treatment, and importers should verify that the applicable tariff shift or regional value content requirements are met when claiming USMCA benefits on Mexican-origin frame parts.