The composition of the pouring system Ordinary runner system, also called runner system, or pouring system, is the necessary passage for molten plastic from the nozzle of the injection machine to the mold cavity. The runner system includes main runners, runners, gates, etc. Mainstream:Also called the main runner, sprue or down runner, it refers to the runner from the part where the nozzle of the injection machine is in contact with the main runner bushing of the mold to the runner. This part is the first part where the molten plastic flows through after entering the mold.