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 parts 3.5 inches (89 mm) and under in nominal cross-sectional thickness, requiring a through-hardening steel capable of developing a minimum hardness of 52 HRC, the parts being subject to very rigid magnetic particle inspection standards. Certain design and processing procedures may cause these products to become susceptible to stress-corrosion cracking after heat treatment; ARP 1110 recommends practices to minimize such conditions.