A Subheading is the six- or eight-digit level within a Heading of the Harmonized Tariff Schedule. The six-digit subheading is internationally harmonized — every country using the Harmonized System shares the same six digits. The eight-digit subheading is U.S.-specific and represents the actual duty rate line.
Subheadings within a heading are designated by single or double dashes (—) preceding the description. A single-dash subheading is "indented" at the six-digit level, while a double-dash subheading is further specified at the eight-digit level.
Under GRI 6, classification at the subheading level applies the same principles used at the heading level — only comparable subheadings (at the same level of indentation) may be compared against each other.