INJECTION MOLDING APPARATUS EMBODYING AN OPEN-TOP MOLD, A ROTATABLE SUPPORT FOR MOUNTING TWO LASTS FOR ALTERNATE DISPOSITION AT A PREDETERMINED DISTANCE ABOVE THE OPEN TOP OF THE MOLD, A CARRIAGE MOUNTING THE ROTATABLE SUPPORT FOR MOVEMENT VERTICALLY WITH RESPECT TO THE MOLD TO BRING THE BOTTOM OF THE LAST LOCATED ABOVE THE MOLD INTO ENGAGEMENT THEREWITH FOR INJECTION OF BOTTOMFORMING MATERIAL, AND MEANS SUPPORTING THE CARRIAGE ON A COLUMN FOR HEIGHTWISE ADJUSTMENT RELATIVE TO THE MOLD TO ACCOMMODATE LASTS OF DIFFERENT HEIGHT.