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The Encyclopedia of Horology

Component record · Escapement

Pallets / Pallet Fork

Verified

In a lever escapement, an assembly combining two jewelled pallet stones set in a steel fork, which alternately locks and releases the escape wheel while communicating impulse to the balance.

What it does

Locks the escape wheel between impulses, receives a push from an escaping tooth, and transmits that impulse to the balance via the fork horns and impulse pin, then returns to lock the next tooth.

How it works

The pallet fork carries two pallet stones, entry and exit, positioned to engage escape-wheel teeth alternately. As the balance swings, the impulse pin on the balance roller enters the fork's slot and moves the fork, unlocking one pallet from an escape-wheel tooth; the freed wheel turns slightly until its next tooth strikes the impulse face of that pallet, delivering a push back through the fork and impulse pin to the balance.

This is a detached escapement: for most of its swing the balance is free of the escapement, connected only briefly during unlocking and impulse, which is central to the lever escapement's superior accuracy compared to frictional-rest designs such as the verge or cylinder.

A safety mechanism — the guard pin and roller table, or an equivalent — prevents the fork from moving to the wrong position (over-banking or mis-tripping) if the watch is jarred, a refinement that made the lever escapement reliable enough for everyday carrying and eventual near-universal adoption.

Evolution

From Mudge's early lever through English detached-lever refinements to the club-tooth, jewelled Swiss lever escapement that became the near-universal standard for mechanical watches by the 20th century.

Known variations

  • English (ratchet-tooth) lever escapement
  • Swiss club-tooth lever escapement
  • Pin-lever (Roskopf) escapement, a economical variant using pins instead of jewelled pallets

Identification for collectors

  • Visible fork straddling the balance roller with two pallet jewels; the club-tooth versus ratchet-tooth escape wheel shape helps distinguish Swiss from English lever variants

Common failure modes

  • Worn or chipped pallet jewels
  • Bent fork horns
  • Worn guard pin allowing mis-tripping

Photographs

Chinese movement escapement and jewels
Chinese movement escapement and jewels — Hustvedt, CC BY-SA 3.0. Wikimedia Commons file page

Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.

Sources & references

  1. Gazeley, W. J., Clock and Watch Escapements
  2. Daniels, G., Watchmaking

Where sources disagree, the disagreement is stated rather than resolved silently.