Bezel

The British Horological Institute, a professional body for watch and clock makers rather than a standards-setting authority, defines the word in the glossary of its Practical Clock and Watch Servicing Distance Learning Course Technician Grade: a bezel is "That part of a watch or clock which holds the glass (or crystal) protecting the dial and hands." That describes the fixed bezel, and it is the only definition of the term this Codex could read in a source it is willing to cite.

A bezel can also be a structural, threaded component. Rolex's own account of its Oyster case states that "A system of screwing down the bezel, case back and winding crown against the middle case ensured that the case was hermetically sealed", and that "The bezel on the original Oyster case was fluted, allowing it to be screwed down onto the middle case using a tool exclusive to Rolex." The Swiss industry treats the bezel as a case part with its own dimensions: the Federation of the Swiss Watch Industry's list of available NIHS standards includes NIHSG 60-21, Boîtes rondes étanches – Carrure-lunette (partie lunette).

The open question. The rotating bezel is the one form of bezel a standard cares about, and its clause has not been read. ISO 6425:2018, Horology — Divers' watches, edition 4, published October 2018, applies to watches "equipped with a secured measuring system to indicate the diving time, which is visible in darkness". On a conventional divers' watch that secured system is the rotating bezel, but the standard's requirements text is paywalled, so the rule that such a bezel may turn in one direction only is neither quoted nor attributed to ISO here.