What kind of part is the 'string stopper' mentioned in the description?

A string stopper refers to a small fastening part that grips the string attached to a garment so that it does not loosen again. If there is only a string, it quickly returns to its original state even when pulled, but if you press the stopper, pull it as much as you want, and release it, it stops right there.

On this nylon jacket, this device is located in two places: the sleeves and the hem^[2]. Tightening the sleeve side narrows the wrist opening, reducing the path for wind to enter and making the sleeves less likely to slip down when you roll up your arms or move. Tightening the hem side gathers the area below the waist, narrowing the silhouette that flares downward. If you leave it loose, the wide fit is preserved as it is, and if you pull it, it takes on a silhouette that fits closer to the body, allowing you to wear the same piece in two different silhouettes.

In terms of care, it is marked not to use a tumble dryer^[3]. In general, auxiliary materials attached to clothing, such as strings and stoppers, can deform or get crushed during high-temperature tumble drying, so it is safer to hang-dry clothes with such tightening devices. For reference, the tightened look in the detailed cuts is based on a 177cm-tall model wearing size M^[4].