the invention concerns a nozzle for the production of hollow bodies of thermoplastic material by extrusion blow molding . according to the invention , continuous extrusion of at least two preforms in web form of plasticized material is effected by means of a plurality of extrusion devices . the preforms are jointly shaped to form a hollow body in the still plastic condition , that is to say , in the first heat , within a multi - part tool forming a mold cavity . in that case , a wall thickness profile is imparted to at least one preform during the extrusion operation independently of the respective other preform by continuous nozzle gap adjustment during the extrusion operation .