This specification covers a premium aircraft-quality, low-alloy steel in the form of bars.

These bars have been used typically for parts required to meet stringent magnetic inspection criteria, having sections 0.50 inch (12.7 mm) and under in nominal thickness at time of heat treatment, and requiring a through-hardening steel capable of developing hardness as high as 35 HRC when properly hardened and tempered and also parts of greater thickness but requiring proportionately lower hardness, but usage is not limited to such applications.