Component record · Regulation
Hairspring Stud
VerifiedA small fixed post that anchors the outer end of the balance spring (hairspring) to the balance cock or stud carrier.
What it does
Holds the outer terminal coil of the balance spring stationary, so that the spring can flex between this fixed point and the balance staff as the balance oscillates.
How it works
The hairspring's outer coil terminates in a small collar or bent end that is clamped or pinned into a slot in the stud, fixing that end of the spring in place.
The inner end of the spring is similarly fixed, via a collet, to the balance staff, so the spring winds and unwinds between these two fixed points as the balance turns.
In free-sprung movements, the stud is sometimes mounted on a rotatable carrier that can be adjusted for the spring's overall position without needing a separate curb-pin index for day-to-day rate adjustment.
Evolution
Stud design has evolved alongside overall balance-spring and regulation systems, with movable stud carriers becoming a feature of high-grade free-sprung movements seeking to minimise curb-pin friction.
Known variations
- Fixed stud on the balance cock
- Rotatable stud carrier in free-sprung designs
Identification for collectors
- Small block or post on the balance cock where the hairspring's outer end terminates
Common failure modes
- Stud coming loose, allowing the hairspring to shift position and disrupt timing
- Spring end breaking at the stud pinning point from fatigue
Related photographs
No confidently matched photograph of this subject has been found yet. These photographs show a closely related record, and are not examples of the type described on this page.
Sources & references
- Daniels, G., Watchmaking
Where sources disagree, the disagreement is stated rather than resolved silently.