A blow molding apparatus wherein an extruded tubular parison is pressurized to form a molded article, comprises a blow pin for introducing pressurized fluid into the parison, an actuator for advancing and retracting the blow pin and adjusting means for determining the orientation of the actuator to achieve substantial parallelism of a blow pin shaft to which the blow pin is attached and a centerline of the opening through a forming die through which the blow pin shaft passes and to achieve substantial parallelism of a sealing element of the blow pin with a plane transverse to the opening of the parison.