The Balance Spring
Collet and Overcoil
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The collet (green arrow) sits on the balance shaft
and attaches the inner end of the balance spring to the balance shaft. In this illustration, the balance spring is an overcoil design, the overcoil indicated in yellow. The blue triangle represents the
spring stud on the balance cock.
Although the overcoil design (also know as a “Breguet spring”) is not often used in contemporary wristwatches because of its susceptibility to shock, it prevents shifting of the center of gravity of the spring during
balance rotation and improves positional adjustment of the watch.
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