Sprue (manufacturing) - Injection Molding - Gates and Runners

Gates and Runners

Some moldmakers make a distinction between three separate entities: the gate, the runner, and the sprue. Certainly in the plastics injection moulding industry, the gate is the location at which the molten plastic enters the mold cavity and is often seen as a small nub or projection (the "gate mark") on the molded piece. The sprues are large-diameter channels through which plastic flows, usually around the edges of the part or along straight lines. Finally, in this naming scheme, the runner represents only the smaller channels that divert from the sprue to the individual part. An analogy to the sprue/runner system might represent the sprues with city water mains, and runners with the smaller pipes leading to individual houses.

Many scale model kits are made from injection-molded plastic. Hobbyists, such as builders of scale models, typically remove the parts of a model kit from the runner using a sharp craft knife or razor saw. They may also use the sprue or runner as a raw material to fabricate additional parts, such as railings on model ships, or antenna wires on airplanes.

Sprues in model kits often include engravings to identify the parts by number.