7320.90.10.00 - Hairsprings

This HTS category, 7320.90.10.00, specifically covers hairsprings made of iron or steel. Hairsprings, also known as balance springs, are very fine, coiled springs essential for the proper functioning of mechanical watches and other timekeeping devices. Their primary purpose is to regulate the oscillation of the balance wheel, thereby controlling the rate at which the timepiece runs. Due to their delicate nature and precise manufacturing, they are distinct from other types of springs found in Chapter 73.

This classification is distinguished from its sibling category, 7320.90.50, which covers "Other" springs and leaves for springs of iron or steel that do not fit into more specific subheadings. While 7320.90.10.00 is exclusively for hairsprings, 7320.90.50 acts as a residual category for all other iron or steel springs not otherwise classified, such as larger or more robust springs used in machinery or vehicles.

As this is a leaf node in the HTS structure, there are no further subcategories. Classification under 7320.90.10.00 is therefore directly determined by the item being identified as a hairspring for use in timekeeping mechanisms, manufactured from iron or steel, and not falling under any more specific provision.