An undercut refers to part features that prevent straight ejection at the parting line. Undercuts cause mold complexity and therefore lead to higher mold construction and maintenance costs. If possible, it’s preferred to redesign the part to avoid undercuts. Shown in Figure 1, to form the rectangular opening to the left, a retractable core is required. However, by extending the opening all the way through the top surface, it can be formed by a static core moving in the draw direction of the tool.