Additional U.S. Rules of Interpretation

The Additional U.S. Rules of Interpretation are four U.S.-specific rules appended to the General Rules and printed at the front of the HTSUS. They govern classification beyond the international 6-digit level — that is, at the 8-digit subheading and 10-digit statistical suffix levels.

The four rules:

1. Rule 1(a) — A tariff classification controlled by "use" (other than actual use) is determined by the principal use of the class or kind of goods to which the merchandise belongs.
2. Rule 1(b) — An actual use classification requires the goods actually be used as specified, with proof of use.
3. Rule 1(c) — A specific eo nomine provision prevails over a "parts" provision unless explicitly stated otherwise.
4. Rule 1(d) — The terms "wholly of," "almost wholly of," "of," "containing," and similar phrases have specific defined meanings.

Together with the General Rules of Interpretation, the Additional U.S. Rules form the legal foundation of every U.S. classification decision.