Component record · Regulation
Hairspring Collet
VerifiedA small collar, split or friction-fitted, that clamps the inner end of the balance (hair)spring to the balance staff.
What it does
Anchors the balance spring's inner coil concentrically to the balance staff so that the spring can wind and unwind evenly about the staff's axis as the balance oscillates.
How it works
The collet grips the balance staff, usually by a friction fit or a split-and-clamped design, and the innermost coil of the balance spring is pinned or otherwise secured to the collet, fixing the spring's centre point precisely on the staff's axis.
Correct collet position and truth (concentricity) are essential: an off-centre or tilted collet throws the whole balance spring out of true, causing the coils to touch each other or the balance arms during oscillation and badly disturbing timekeeping.
Adjusting a balance spring for correct beat (so the balance's rest position aligns properly with the escapement's locking geometry) is frequently done by carefully rotating the collet on the staff, a delicate procedure central to 'putting a watch in beat'.
Evolution
The collet's basic function has remained constant since the balance spring's introduction, though modern manufacturing achieves far tighter concentricity and reduces the delicate hand-fitting once required.
Known variations
- Split (friction) collet
- Solid collet secured by a small screw or pin
- Integral collet-and-spring assemblies in some modern manufacturing methods
Identification for collectors
- The small collar visible at the base of the balance spring's coils where they meet the balance staff
Common failure modes
- Loose collet slipping on the staff, throwing the watch out of beat
- Off-centre or tilted collet causing coils to touch and rate to become erratic
- Broken pinning point where the spring's inner coil attaches to the collet
Photographs
Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.
Sources & references
- de Carle, D., Practical Watch Repairing
- Daniels, G., Watchmaking
Where sources disagree, the disagreement is stated rather than resolved silently.