Springs for clocks, watches, and similar precision instruments are classified in the chapter covering clocks and watches or measuring instruments, not here. Heading 7320 covers springs of iron or steel for general industrial, automotive, and mechanical use. The intended application and the chapter notes for precision instruments govern the boundary.

If the spring itself is the essential component and the non-steel elements are ancillary (such as rubber end caps or plastic retainers), the assembly generally follows the spring's classification under heading 7320. However, if the non-steel element gives the article its essential character or if it is more specifically described by another heading, reclassification may apply. A binding ruling is advisable for composite spring assemblies imported regularly.