Form: This specification covers an aircraft-quality@ low-alloy steel in the form of bars@ forgings@ and forging stock. Application: Primarily for parts with sections 0.875 in. (22.225 mm) or less in thickness at the time of heat treatment which require a through-hardening steel capable of developing hardness as high as 50 HRC when properly hardened and tempered and also parts of greater thickness but requiring proportionately lower hardness. In appropriate section sizes@ this material is capable of meeting the requirements of AMS 2310.