Heading 5004 covers silk yarn (not spun from waste) in bulk industrial packaging — cones, cheeses, or hanks intended for further manufacturing. Heading 5006 covers the same yarn when put up for retail sale in small quantities for home sewing or craft use, as well as yarn spun from silk waste in retail packaging and silkworm gut. The packaging and intended end-user determine which heading applies.

Key specifications include denier (filament fineness), number of plies, twist direction and turns per meter, and whether the yarn is raw (with sericin) or degummed. These parameters affect both the applicable tariff line and the yarn's suitability for specific weaving or knitting applications, so accurate technical documentation supports both classification and buyer acceptance.