An extruder head for extrusion blow-molding plastic containers includes a ring gap nozzle with a mandrel and a ring-shaped nozzle body. An elastically deformable sleeve is arranged on an end of the nozzle outlet side and defines a gap width which can be varied by axial setting movements of the mandrel and/or the nozzle body. The geometry of the nozzle gap can be influenced by radially deforming the sleeve with setting devices during the extrusion of a hose-shaped preformed blank. The sleeve may be moved in a radial direction and is guided on sliding surfaces which support it in upward and downward directions. The sleeve may be in the form of a cylinder or tube. A lower edge of the sleeve shapes a cross-section of a melt stream exiting from the ring gap nozzle.