It is a groove outlet in the mold to discharge the original and molten gas. When the melt is injected into the cavity, the air in the cavity and the gas brought into by the melt must be discharged at the end of the material flow through the vent to the outside, otherwise it will make the product with pores, bad connection, filling the mold dissatisfaction, or even accumulate air due to compression produced by heat and burn the product. In general, the vent hole can be located at the end of the melt flow in the cavity, but also on the parting surface of the mold. The latter is a shallow groove with a deep 0.03-0.2mm and wide 1.5-6mm on the side of the die. In the injection, the vent hole will not have a lot of molten material seeping out, because the melt will be in the cooling and curing of the channel blocked. The opening position of the exhaust vent should not be to the operator, in case the melt accidentally sprayed out the injured person. In addition, the ejector rod and the ejector hole with the gap between the top and the release plate and the core of the mating gap to exhaust.