Various embodiments are disclosed herein that relate to the molding of an item having a non-uniform thickness and an undercut structure. One disclosed embodiment provides an injection molding device for molding a part having a non-uniform thickness and an undercut structure, the injection molding device comprising a pair of opposing end walls, a first mold surface being stationary with respect to the pair of opposing end walls, and a second mold surface being movable toward the first mold surface such that a first end of the second mold surface is movable a larger travel distance toward the first mold surface than a second end during a molding process. Further, the pair of opposing end walls comprises a slider with an undercut mold surface that is movable in a direction transverse to a direction in which the second mold surface is movable toward the first mold surface.