Radially spaced magnets
Six pairs of custom circles with 3, 5, 6, 8, 12, or 16 evenly spaced magnets each, and with either the first magnet, or the first side of the magnet polygon, at the top. For numbers of magnets other than 2, 4 and 8, the OmniGraffle 5 Connections Inspector doesn't allow for radially even distribution of magnets. (The N-magnets-per-side options concentrate the magnets on the four cardinal sides, leaving blind patches at the corners). For some purposes, getting a link to approach a shape at the right angle depends on magnets that have radially even spacing. It may be helpful to toggle the View > Magnets option in the OmniGraffle menu while using these shapes.