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Attraction between a pair of rare earth-cobalt magnets is very useful for retention of dental prosthetic appliances. In these applications, the space available for embedding magnets is very narrow. Therefore, the magnets must have those optimum dimensions which cause the mximum attraction. The optimum dimensions are calculated for a rectangular or disk magnet pair utilizing the axial or radial attraction. In order to maximize the axial attraction of a magnet pair in small separation, the rectangular magnet must be slender and the square or disk magnet must have a size ratio of about OA, which is defined as the ratio of thickness to length of edge or diameter of the magnet. In the case of radial attraction, the optimum disk magnet has a little larger size ratio, e.g., about 0.55 in zero separation. Based on these theoretical analyses, the method of designing the optimum magnets with a required attraction is proposed.