This manual was developed to provide basic information and recommend sources of additional information pertaining to metallic gear materials, their treatments, and other considerations related to the manufacture and use of gearing. The gearing application conditions, including allowable stresses, environment, component geometry, and component weight limitations, must be understood to select the proper gear material. Metallurgical aspects of gearing as related to rating (allowable contact stress number and allowable bending stress number) are not included, but are covered in AGMA rating standards.