There are those importers who find themselves under the belief that duty rates are beyond their control. However, one of the ways an importer can use his or her whit and intelligence is known as "Tariff Engineering."
The importing laws in the United States are for the most part narrowly tailored to a specific item. For example, you import an adult bicycle and there is a tariff duty rate for that bicycle. However, this strict construction of items based on a tariff may benefit the importer. That same adult bicycle may have different duty rates based on its wheels diameter!
The laws in the U.S. provide a framework for how to import your goods. During the manufacturing process the importer is recommended to speak with the manufacturer, customs broker, and/or attorney to determine the most cost effective way of manufacturing the product to save on import duties - i.e. Tariff Engineering. The earlier this is done in the production process the more one can predict how Customs will react to the product during importation.
Planning is the key word folks - you do not want to the surprise of owing thousands in duty after the goods left the dock.