Chrome vanadium steel for strength and durability and precision broached jaws for sure gripping. Thin walled construction for access in cramped quarters and heat treated for consistent hardness. 12-point box end for snug fit. Meets ANSI standards. Imperial 11 piece set includes: 1/4", 5/16", 3/8", 7/16", 1/2", 9/16", 5/8", 11/16", 3/4", 13/16", 7/8".