The classification of products for US Customs purposes is done so by using a hierarchical process as outlined by the General Rules of Interpretation (GRI). Per GRI 1, the classifier must review any notes or exclusions that may be listed in the corresponding section and chapter notes.
After considering GRI 1, go to GRI 2. Per GRI 2, the classifier will choose to classify an incomplete or unfinished product (e.g. an unassembled bicycle) as if it were complete.
After considering GRI 2, proceed to GRI 3. GRI 3 has three parts, and is used when an article consists of more than one substance (e.g. an mp3 player packaged with headphones). Per GRI 3a, a more descriptive classification of one part of the article is preferred to a less descriptive classification of the other part(s). Per GRI 3b, choose to classify the product based on the part of the article that gives it its essential character (e.g. the mp3 player gives the set its essential character, because the headphones are relatively incidental). Per GRI 3c, all other things being equal, choose the classification that occurs last in the harmonized tariff schedule.
If the article cannot be classified using the before-mentioned GRI’s, then proceed to GRI 4. Per GRI 4, the article can be classified as an article most akin to it if otherwise unable to classify. This can occur when fundamentally new products are introduced into the market (e.g. new high-tech devices).
Finally, GRI 5 explains that cases (e.g. camera cases, musical instrument cases, etc.) will be classified the same as the article for which they would contain (i.e. as cameras, musical instruments, etc.), UNLESS the case has its own essential character. An example of a case with its own essential character may be fine leather business card holder. It would be classified as a leather product rather than as if it were a business card.