Component record · Regulation
Regulator Boot
Partially verifiedA small sliding piece on some regulator indexes that supports the balance spring near the curb pins, reducing distortion of the coil as the index is moved.
What it does
Cradles the hairspring alongside the curb pins so the spring is guided rather than merely pinched, helping keep its coil concentric and reducing positional rate errors introduced by the regulator.
How it works
Where a plain curb-pin index only pinches the spring between two pins, a boot-equipped index adds a supporting surface that the spring's coil rests against, distributing the contact more gently across a small arc rather than two point contacts.
This reduces the risk of the curb pins locally distorting the coil's shape, a distortion which can otherwise degrade isochronism (the tendency of the balance to keep the same rate regardless of amplitude).
Evolution
Boot-and-pin regulator designs represent an intermediate refinement between simple curb-pin indexes and the friction-free approach of fully free-sprung balances, which dispense with a curb-pin index altogether.
Known variations
- Boot combined with a conventional two-pin curb
- Free-sprung designs omitting boot and pins entirely
Identification for collectors
- A small additional shaped piece alongside the curb pins on the regulator index, visible under magnification
Common failure modes
- Wear or distortion of the boot surface altering its supporting action
- Misalignment causing the spring to bind rather than glide
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., Watch and Clock Encyclopedia
- Terminology and exact prevalence of 'boot' regulator designs vary between sources; treat as a documented but less universally standardised regulator refinement.
Where sources disagree, the disagreement is stated rather than resolved silently.