Form This specification covers an aluminum alloy in the form of sheet 0.008 to 0.126 inch (0.20 to 3.20 mm)@ inclusive@ in nominal thickness@ with a grain size of ASTM No. 6 or finer (see 8.5). Application This sheet has been used typically for severely formed structural parts which will be subsequently heat treated and painted or otherwise protected from corrosion@ but usage is not limited to such applications.