a type of finishing also sometimes referred to as a “spiral” decoration that is generally applied to components such as ratchet wheels and barrel covers. The decoration is created by grinding a wheel that is rotated over the surface of a part in a way that a spiral-shaped pattern is achieved.

References:

Website – https://www.circuitousroot.com/artifice/machine-shop/surface-finishing/snailing/index.html

Book – Audemars Piguet book “High-end horological finishing and decoration”