Glossary · Regulation
Impulse pin (roller jewel)
A small jewel or pin fixed to the balance roller that engages the pallet fork's notch.
Explanation
The impulse pin (roller jewel) is the small jewel fixed in the balance roller that engages the notch of the pallet fork, receiving impulse from the escapement and unlocking it in return. A loose, chipped or shellac-failed pin causes erratic escapement action; pins are traditionally refixed with shellac.