This expert set is manufactured from the highest quality Chrome Vanadium steel. Perfect for the mechanic engineer boat and aero workshops. Specification: Hardened and tempered. Manufactured from the highest quality chrome vanadium steel 6140. Expert quality. Comes in storage pouch. Sizes: 3/8" 7/16" 1/2" 9/16" 5/8" 11/16" & 3/4"