Divider pad
A divider pad (a layer pad): a flat sheet of board laid between two layers of products in a case, or on its floor or under its top, to spread the load and keep the layers apart. Its corners can be cut off at 45° so it drops in past the case's corner joints, and it can have a lifting tab at each end that folds up, to lift it out by. Sizes are the inside sizes of the case it goes in (L × W) and the tabs' height (D). The board's thickness (T, chosen as the material) is allowed for: the pad is T smaller each way than the case, so it drops in.
At its own sizes
Open it in ParametrIQ CAD
It comes with ParametrIQ CAD: File › Run Parametric… › Packaging › Divider pad. Or download its drawing file (.piq) and open it in CAD.