The material is the dividing line: 7303 covers tubes and pipes made from cast iron (produced by pouring molten iron into a mold), while 7304 covers seamless tubes of iron other than cast iron or steel, and 7306 covers welded forms. Ductile iron pipe, which is a form of cast iron, also falls under 7303.

Cast iron pipes and tubes are subject to Section 232 tariffs on iron and steel articles. Antidumping or countervailing duty orders may also apply to specific product types from specific countries; importers should check the current order list at the time of entry.