Below is a picture of a gas-assist test mold used to manufacture automotive cooling pipes. It contains three overflow cavities and two gas needles. Gas-assist molds can be made from similar materials to standard injection molds. However, lower tonnage can be expected in most cases, so aluminum molds may be a consideration for smaller production runs. For higher volume parts and more aggressive plastics, more wear resistant tool steels should be utilized.

The position of the gas needle (or pin) is critical to the gas-assist process. The gas needle should penetrate the cavity from 1/3 to 1/2 of the gas channel thickness, unless a boss configuration is utilized. The plastic must seal around the gas needle prior to gas injection, or the gas will leak between the part and the cavity wall, through the vent to atmosphere. This will not only cause quality problems, but will be a waste of the nitrogen gas. The gas needle should be removable from the face of the mold, in order to avoid dismantling the mold, if a gas needles plugs. The diameter of the gas needle and the size of the supply hose are also a concern. They affect the volume of gas entering the gas channel and the response time of the gas injection.