A hair spring is a small, coiled piece of metal used in various mechanical devices, particularly in watches. It is designed to store and release energy, allowing the watch to keep accurate time. The hair spring is crucial for the movement of the watch's gears, ensuring they operate smoothly and consistently. In the context of watchmaking, the hair spring is often made from a special alloy that resists temperature changes and wear. This component is also known as a balance spring and works in conjunction with the balance wheel to regulate the timekeeping of the watch.