An extrusion blow mold machine forming hollow containers. The machine has at least one pair of opposing half molds that combine to form a mold and define a mold cavity. Each of the half molds is positioned on a carrier plate and includes first, second, and third mold segments. The first and third mold segments can move with respect to each other and with respect to the second, fixed mold segment. A mechanical structure creates vertical movement of the first and third mold segments relative to the second mold segment as the mold opens horizontally, without the aid of any electrical, hydraulic, or pneumatic device. A closing unit engages the carrier plate to move the carrier plate and its respective half mold toward and away from the opposing half mold and its respective carrier plate, thereby closing and opening the mold.

A blow-molded plastic structure may include an inwardly extending portion with an undercut. The inwardly extending portion may be disposed in an outer surface of the blow-molded plastic structure and the undercut may be disposed in the inwardly extending portion. The structure may be formed by placing a tool in a mold, forming a parison of molten plastic, disposing the parison of molten plastic in the mold, closing the mold around the parison of molten plastic, inflating the parison, and creating an inwardly extending portion with an undercut with the tool during the blow-molding process. The tool used to create the undercut in a blow-molded plastic structure may include a base, one or more guides, and one or more fingers movable relative to the base between a molding position and a release position. The fingers may include an elongated body and an outwardly extending portion.

An extrusion blow mold machine forming hollow containers. The machine has at least one pair of opposing half molds that combine to form a mold and define a mold cavity. Each of the half molds is positioned on a carrier plate and includes first, second, and third mold segments. The first and third mold segments can move with respect to each other and with respect to the second, fixed mold segment. A mechanical structure creates vertical movement of the first and third mold segments relative to the second mold segment as the mold opens horizontally, without the aid of any electrical, hydraulic, or pneumatic device. A closing unit engages the carrier plate to move the carrier plate and its respective half mold toward and away from the opposing half mold and its respective carrier plate, thereby closing and opening the mold.