Yarn is considered put up for retail sale when it is packaged in a form clearly intended for sale to end consumers — small labeled spools, skeins with hang tags, or blister-packed quantities typical of craft or sewing retail. Industrial cones, large cheeses, or unlabeled bulk hanks intended for textile mills are not retail-packaged and belong under headings 5004 or 5005.

Silkworm gut is produced from the silk gland of the silkworm larva before it spins its cocoon, drawn into a monofilament strand. Historically used for surgical sutures and fine fishing lines, it is grouped with retail silk yarn in heading 5006 because both are finished, consumer-ready silk-derived products rather than industrial fiber inputs. Its trade volume today is very small.