Aluminum doors and windows, including their frames and thresholds, are specifically named in subheading 761010, so a complete window unit with its frame is properly classified here. The exclusion for prefabricated buildings (heading 9406) applies to entire modular building sections, not to individual window or door units. If the assembly includes non-aluminum components that give it the character of a different article, a more specific heading may apply.

Profiles are semi-finished products with a uniform cross-section not yet worked into a specific structural application. Once profiles are cut to length, drilled, punched, or assembled into a recognizable structural component — such as a curtain wall mullion system or a bridge truss section — they take on the character of a structure or part thereof and belong here. The extent of further working and the specificity of the intended application are the key factors.