In the design of high speed, fine pitch wire matrix print heads, magnetic characteristics and the structure of the armature are studied. Design conditions are proposed for minimizing the equivalent mass. Several armature models are evaluated empirically and non-grooved armatures are found to be suitable for large magnetomotive forces, while grooved armatures offer a slight performance advantage for small magnetomotive forces. The armature magnetic circuit model is then analyzed numerically. As the average flux density increases, magnetic saturation occurs first at the root of the core, and then extends to the inner core portions and the armature. The magnetic attractive force acting on the armature is calculated taking magnetic saturation into account. In order to minimize the mass of the armature, lever, and wire, the lever ratio, which is the ratio of wire rotation radius to armature rotation radius, is taken as a design parameter. It is shown that there exists an optimum lever ratio which minimizes the equivalent mass, and the effects of lever shapes are clarified.