Recently, design support tools have been used to improve the efficiency of design work. These tools support design verification at each design stage, and succeed to some extent in improving the efficiency of the design work. However, the management of scattered design information and data conversion have lately become difficult because designers often require two or more tools. In this paper, we focus on the detailed design of mechanism parts made by injection molding and used in precision consumer products. We propose a design product model which describes the detailed design of such parts. The model describes the mechanism parts based on sets of faces, which are basic units in design work. In this way, the model can express design information in both two- and three-dimensional forms. We also define the procedures used to operate the model. Finally, the effectiveness of this model is shown by applying it to an experimental system.