Abstract: A tool box has an upstanding side wall structure which may have a front opening to receive one or more drawers, the side wall structure being closed at the upper end by a top panel and at the lower end by a unitary, one-piece bottom panel. The bottom panel has three parallel depending ribs deformed from the plane of a base wall, with one rib disposed along a front edge of the base wall and being unitary with an upstanding front flange with a rearwardly extending lip. Side flanges, spaced apart by the ribs, depend from each side edge of the base wall. In one embodiment a rear flange depends from the rear edge of the base wall and in a second embodiment a channel-shaped upstanding rear wall is provided. The flanges and rear wall of the bottom panel provide means for attachment thereof to the side panel structure and slots are provided in the bottom panel for attachment of casters.