Form: This specification covers an aircraft-quality@ low-alloy steel in the form of bars@ forging@ flash welded rings@ and stock for forging or flash welded rings. Application: Primarily for parts@ 0.75 inch (19.0 mm) and under in nominal section thickness at the time of heat treatment@ requiring a through-hardening steel capable of developing hardness as high as 40 HRC when properly hardened and tempered and for parts of greater thickness but requiring proportionally lower hardness.