Component record · Escapement
Impulse Jewel (Roller Jewel)
VerifiedA small pin, usually of synthetic ruby or sapphire, projecting from the roller table and engaging the pallet fork's slot.
What it does
Carries impulse between the pallet fork and the balance during each half-oscillation, and also unlocks the pallet fork by entering its slot.
How it works
As the balance swings, the impulse jewel enters the pallet fork's slot, unlocking the escapement and receiving an impulse from the escape wheel via the fork before leaving the slot again on the far side of the swing.
The jewel's hardness and polish minimise friction and wear at this high-cycle contact point, which is engaged roughly five times per second in a typical 18,000 vibrations-per-hour watch.
Correct alignment and depth of the impulse jewel relative to the fork slot is essential; misalignment causes poor impulse transfer, banking errors, or the escapement stopping (knocking or setting).
Evolution
The move from natural garnet or other early jewel materials to synthetic ruby, standardised in the 20th century, improved consistency and reduced cost.
Known variations
- Round impulse pin (most common)
- D-shaped or other profiled impulse pins in some designs to alter the impulse geometry
Identification for collectors
- Visible as a small jewel pin on the roller table under magnification
Common failure modes
- Chipped or cracked jewel from shock
- Loose jewel in its setting, causing erratic impulse transfer
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.