A simple model is used to optimize the design of permanent magnet, coaxial, force couplers. Two configurations (with and without flux-closure yokes) are analyzed and design parameters are given for maximizing either coupling force or stiffness per unit volume of magnetic material. The model is also modified to the case of magnetic bearings. By means of the theorem of Brown and Morrish, it is shown that the performance of yokeless radially and axially magnetized couplers or bearings is the same. The technological implications of this result are noted.