This specification covers a premium aircraft-quality, low-alloy steel in the form of bars, forgings, mechanical tubing, and forging stock. These products have been used typically for carburized parts requiring high minimum core hardness in sections 0.375 inch (9.52 mm) and under in nominal thickness, and which are subject to rigid magnetic particle standards, but usage is not limited to such applications. The core may or may not be machinable after hardening.