9102.21 - With automatic winding:

This HTS category, 9102.21, specifically covers wrist watches that feature an automatic winding mechanism. Automatic winding means the watch is powered by the natural motion of the wearer's wrist, which winds the mainspring without the need for manual winding. This classification applies to such wrist watches, regardless of whether they include a stopwatch function.

It is important to distinguish this category from its sibling, 9102.29, which covers "Other" wrist watches. Category 9102.21 is exclusively for automatic winding watches. If a wrist watch does not have automatic winding (e.g., it requires manual winding or is battery-powered quartz), it would generally fall under 9102.29. The defining characteristic here is the automatic winding mechanism.

The subcategories within 9102.21 further refine the classification based on the number of jewels present in the watch's movement. These subdivisions are: "Having no jewels or only one jewel in the movement," "Having over one jewel but not over 17 jewels in the movement," and "Having over 17 jewels in the movement." The presence and quantity of jewels in the movement are critical for distinguishing between these specific subcategories, as jewels serve to reduce friction and improve the longevity and accuracy of mechanical watch movements.