The Geneva Seal Rules 7–9: Pinions, Escape Wheel & Pallet Fork
This is Part 3 of our 4-part series on the Geneva Seal — the 12 strict rules that define the pinnacle of Swiss watchmaking. In this article, we cover Rules 7 through 9.
← Part 1: Rules 1–3 | ← Part 2: Rules 4–6
Rule 7: Steel Pinions
All steel pinions of the gear train, their cross-sections, all pivot ends, and their arbors must be mirror-polished. In other words, every wheel in the gear train must be beveled and polished, and all steel pinion leaves — including every surface — must be mirror-finished to a brilliant shine.
This level of finishing serves a critical functional purpose: when ruby jewels and pivots are both mirror-polished, friction is dramatically reduced. Lubricating oil, rather than spreading and evaporating due to capillary action on rough surfaces, forms a perfect spherical droplet held in place by surface tension — ensuring long-lasting lubrication and precision.
Fig. 1-3-9: All steel pinion leaves and pivot ends must be mirror-polished.
Rule 8: The Escape Wheel
Within the lever escapement system, the escape wheel must be lightweight, and the pallet fork itself should ideally have a balance device. For movements with a diameter greater than 18mm, the escape wheel thickness should not exceed 0.16mm. For movements smaller than 18mm, the thickness must not exceed 0.13mm.
The locking surfaces of the escape wheel teeth that engage the pallet stones must be polished. The impulse faces of the teeth that drive the pallet stones must be mirror-polished. Only with this level of finishing can friction be effectively minimized, preventing oil from spreading due to capillary action.
The ideal locking depth between the escape wheel and pallet stones should be 0.07–0.10mm. The smaller the contact area, the less energy is lost to friction, and the more efficiently energy is released — resulting in superior timekeeping performance.
Fig. 1-3-10: Escape wheel teeth locking and impulse surfaces must be mirror-polished.
Rule 9: The Pallet Fork
In a lever escapement system, the pallet fork swings left and right to release energy and drive the balance wheel. The positioning mechanism that stops the pallet fork must be controlled by a fixed-type plate — either the main plate or a fork plate is acceptable — but no freely movable or adjustable components are permitted.
The most refined solution uses two ruby stones as the positioning limit structure. The use of adjustable eccentric screws for the banking pins is strictly prohibited. A cylindrical banking pin as the positioning mechanism is not permitted under the Geneva Seal, as its position can too easily be altered by external force. Limit pins are not allowed.
Fig. 1-3-11: The pallet fork positioning mechanism must use fixed ruby banking stones — no adjustable limit pins permitted.
These three rules reveal a deeper truth about the Geneva Seal: it is not merely about beauty. Every finishing requirement exists to reduce friction, preserve lubrication, and protect precision over decades of use.
At Aorawa Time, we are inspired by this philosophy — that true quality is built to last.