Form: This specification covers a premium aircraft-quality@ low-alloy steel in the form of bars@ forgings@ mechanical tubing@ and forging stock. Application: Primarily for critical bearing components requiring a through-hardening steel@ usually with hardness of approximately 60 HRC and section thicknesses of 0.40 to 0.80 inch (10.2 to 20.3 mm)@ and subject to very rigid inspection standards.