Abstract: An improved adjustable diehead assembly for mounting on a plastic extrusion machine is described. A discharge orifice for a parison of plastic is formed by a mandrel and annular member. The annular member is moveable by a holder assembly perpendicular to axis of the mandrel to adjust the orifice. The holder assembly includes cams which act upon the opposed sections of the outside surface of the annular member to adjust the orifice when first and second screws are tightened. A third screw acts upon the annular member to adjust the orifice. The screws are mounted on a front part of the holder assembly on the diehead to allow adjustment of the orifice even when the extrusion machine is operating.