7304.29.31.80 - Having an outside diameter exceeding 406.4 mm

This HTS classification covers seamless pipes and tubes made from iron or steel, specifically of the kind used for drilling oil or gas. Within this broader category, the "Casing" subgroup pertains to tubes used to line the wellbore. Further narrowing, this specific classification focuses on casing made of "other alloy steel" (i.e., not primarily carbon steel) that are "threaded or coupled" for connection.

The critical differentiator for this category lies in its **outside diameter**. It specifically includes casing where the outside diameter **exceeds 406.4 mm**. This distinguishes it from sibling categories that cover casing with smaller outside diameters, such as those less than 215.9 mm, between 215.9 mm and 285.8 mm, or between 285.8 mm and 406.4 mm. Therefore, the precise measurement of the pipe's outer circumference is paramount for accurate classification into this particular code.

As this node represents a leaf in the HTS structure, there are no further subdivisions. Classification under HTS 7304.29.31.80 is final based on the material (other alloy steel), the connection type (threaded or coupled), the intended use (oil and gas drilling), and the specific outside diameter exceeding 406.4 mm. Importers and exporters must ensure all these criteria are met to correctly classify their goods within this code.