the apparatus includes a blow mold for forming a hollow plastic article from a parison including at least two reciprocable mold portions movable from an open position to a closed position , a holding device for holding the parison within the blow mold , and first and second locking portions affixed to the holding device and blow mold portions , respectively , engagable with each other when the blow mold portions are in a closed position to align and clamp the holding device to the blow mold , whereby blowing force is transmitted to the engaged locking portions .