The “Anti-Flex Assembly” is an assembly for maintaining axial stability in a rotatable, expandable and collapsible drum used in tire manufacturing. A cylindrical rod with at least one helical groove is defined in the outer surface of the cylindrical rod and at least one hardened dowel is aligned so as to protrude into the helical groove of the cylindrical rod. A means to maintain the orientation and protrusion of the hardened dowel protruding into the helical groove(s), and a clamping lock is provided to lock the cylindrical rod in place once the desired width of the rotatable, expandable and collapsible drum has been set, thus providing axial stability of the rotatable, expandable and collapsible drum during tire carcass manufacturing.