This document provides nomenclature for general modes of gear tooth wear and failure. It classifies, identifies, and describes the most common types of failure and provides information that, in many cases, enables the user to identify failure modes and evaluate the degree or change from original condition.

This document is based on experience with steel gears; however, many of the failure modes discussed apply to gears made from other materials. Not all failure modes that can occur on other types of gears, such as plastic, bronze, or powder metal gears, are included.

The solution to many gear problems requires detailed investigation and analysis by specialists and is beyond the scope of this document.

This document specifies only the terminology intended to help with the identification and reporting of the appearance and conditions of gears after a period of operation. Neither causes nor preventive measures for any condition described are discussed.

In this document, gear refers to both gear wheels and pinions, unless the gear is specifically identified.

This document does not define “gear failure”.