Classification starts with the text, not the thing. GRI 1 says a product is classified by the terms of the headings and by the section and chapter notes, and that rule alone settles more than 90 percent of products. The importer's first job is to read the heading text and the notes, not to argue about what the product feels like.
The notes are where most disputes are won and lost. A chapter note can exclude a whole category from a heading, or pull a product into a heading it does not look like it belongs in. A product that fits two headings usually fits one of them only if you skip the notes, and the notes are part of the heading for classification purposes.
There are six General Rules of Interpretation, and they apply in sequence. GRI 1 is the terms of the headings and the notes. GRI 2 covers incomplete and unassembled goods, and mixtures. GRI 3 is the tiebreaker for goods that fit two headings. GRI 4 is the most akin rule for goods that fit none. GRI 5 covers cases and packing. GRI 6 applies the whole sequence again at the subheading level.
The order is the point because each rule only applies when the earlier ones cannot decide. A classifier who jumps to GRI 3 has skipped the question GRI 1 was supposed to answer, and the answer they reach is not a classification, it is a guess with a rule number attached. CBP rulings come back to this constantly: apply the rules in order, and most of the argument disappears.
When GRI 1 cannot decide, GRI 3(a) takes the most specific heading over the general one. A heading that names the product beats a heading that describes a class it belongs to. If both headings are equally specific, GRI 3(b) looks for the essential character, the feature that gives the product its identity, and classifies by that.
If neither of those decides it, GRI 3(c) takes the heading that comes last in numerical order. That is the one people get backwards, because it feels arbitrary, and it is. It is a tiebreaker of last resort, and it exists precisely because some products genuinely do not have a most specific heading or a clear essential character. When you reach 3(c), the classification is a coin toss with a rulebook, and the honest thing is to say so in the file.
The practical move is a binding ruling. Under 19 CFR Part 177, an importer can ask CBP for a ruling on a specific product, and the ruling binds CBP on that product. The CROSS database at rulings.cbp.gov holds the published rulings, and it is the first place to look, because a ruling on a near identical product is worth more than any argument about the notes.
File the ruling request with the product in front of you, literally: samples, specifications, photographs, and the exact use. A ruling on a description is worth less than a ruling on the thing itself, and a ruling that comes back against you is still useful, because it tells you the duty before the goods ship instead of after they arrive.
Keep reading: HTS Classification for Apparel: Why the Fabric Decides the Duty, CBP Form 7501: The Fields Importers Get Wrong Most, Customs bond sufficiency: why CBP asks new importers for more.
Apply the General Rules of Interpretation in order. GRI 1, the terms of the headings and the section and chapter notes, settles more than 90 percent of products. Only if GRI 1 cannot decide do you reach GRI 3, which takes the most specific heading, then essential character, then the heading last in numerical order.
GRI 1 is the first General Rule of Interpretation. It says classification is decided by the terms of the headings and by any relative section or chapter notes. The notes are part of the heading, and reading them first resolves most classification questions before the tiebreakers are ever needed.
Essential character is the feature that gives a product its identity, the part that makes it what it is rather than something else. When two headings are equally specific, GRI 3(b) classifies the product by the component or feature that supplies its essential character. It is a judgment call, and it is the most argued part of the tiebreaker.
Request one from CBP under 19 CFR Part 177, with samples, specifications, photographs, and the exact use of the product. The ruling binds CBP on that product. Before requesting one, check the CROSS database at rulings.cbp.gov, because a published ruling on a near identical product may already answer the question.