Every product imported into the United States gets a code from the Harmonized Tariff Schedule, and the code controls the duty rate, the eligibility for trade programs, and the regulations that apply at the border. The schedule is maintained by the US International Trade Commission and searchable free at hts.usitc.gov, but only Customs and Border Protection is authorized to interpret it and issue binding decisions.
Digits one and two are the chapter, the broad product category. Chapter 84 covers machinery, chapter 61 covers knitted apparel, chapter 85 covers electrical machinery. Digits three and four form the heading, the product group inside the chapter. Digits five and six are the international subheading, the code shared by every country that uses the system.
Digits seven and eight are the US subheading, and this is where the money is. The duty rate is published at the eight-digit level, and the rate line is where the MFN rate, the special program rates, and the Column 2 rate for non-NTR countries appear. Digits nine and ten are the statistical suffix, used for trade data reporting only. They do not change the rate, but the entry must report the full ten digits.
The schedule is applied through the General Rules of Interpretation, six rules that are applied in order, plus the Additional US Rules of Interpretation. GRI 1 governs most decisions: goods are classified according to the terms of the headings and any relevant section or chapter notes, working from the four-digit heading down to the specific subheading. The notes can include or exclude your goods outright, and the notes override the heading text.
GRI 3 handles goods that could fall under two headings or are made of mixed materials: the most specific description wins, failing that the component that gives the essential character, failing that the heading last in numerical order. GRI 6 applies the same logic at the subheading level, comparing only subheadings at the same level.
The workable process is the one the Reidel Law Firm lays out: identify exactly what the product is, its material, function, and condition as imported; find the candidate four-digit headings and read the section and chapter notes; apply the GRI in order; then check the WCO Explanatory Notes and CBP's CROSS ruling database for how similar goods have been treated. A CBP ruling on a similar product is the closest thing to a safe answer, and reading it before you rely on it is the step most importers skip.
Chapter 98 holds special classification provisions, such as US goods returned and heading 9802 for articles assembled abroad from US components. Chapter 99 holds temporary legislation and additional duties, which is where the Section 301 tariffs and the Section 232 duties actually live, as 9903 lines.
That is the detail that surprises most importers. The base rate on the product's own line and the additional duties on the chapter 99 line are separate entries on the same summary, and both have to be right. A product classified correctly on its own line and missed on the 9903 line pays the wrong total, and the difference is discovered at liquidation, when the interest has already started.
The schedule contains roughly 19,000 codes, and the duty rates run from zero to over 100 percent depending on the product and the country of origin. There is no shortcut past the reading. Start with the free HTSUS at hts.usitc.gov, read the relevant section and chapter notes, and apply the General Rules of Interpretation from the heading level down. Origin is a separate question from classification, and the two get confused more often than any other pair in the trade.
Digits one and two are the chapter, three and four the heading, five and six the international subheading. Digits seven and eight are the US rate line where the duty is set, and digits nine and ten are a statistical suffix that does not change the rate.
The eight-digit level. The duty rate is published at digits seven and eight. The last two digits are for Census trade statistics, but the entry must still report the full ten-digit number.
Six rules printed at the front of the HTSUS, applied in strict order. GRI 1 governs most decisions: classify by the heading terms and the section and chapter notes. GRI 3 handles goods that fit two headings, and GRI 6 applies the same logic at the subheading level.
In Chapter 99, as 9903 lines. They are additional duties on top of the base rate on the product's own line, and both lines have to be reported on the entry summary.