The heading covers plain, unfitted containers. When a tank is equipped with internal components — such as heating or cooling coils, agitators, pumps, or level sensors — it may take on the character of industrial processing equipment classified under machinery headings. The degree of integration and whether the fittings are essential to the vessel's function guide the analysis; a bare tank with only a simple outlet valve typically remains here.

Capacity is the total internal volume of the vessel, measured in liters regardless of shape. For irregularly shaped tanks, the actual volumetric capacity rather than nominal or rated capacity governs. Importers should ensure that commercial invoices and technical documentation state the actual internal capacity to support the declared classification.