Abstract: A carriage supporting at least one read/write head is displaceable by a rack and pinion drive toward and away from the axis of rotation of a magnetic disk. The carriage has a pair of rollers--one at the inner end of the carriage, the other at the outer end--in contact with a fixed precision guide. The rack is cantilevered from a flexure element projecting from the carriage and formed as an integral part of the carriage. The free end of the rack is resiliently biased so as to urge (i) the rack into firm, meshing engagement with the pinion and (ii) the carriage rollers into positive, preloaded engagement with the guide. The limits of carriage motion and spacing between rollers are such that the line of force between the rack and pinion is always intermediate the axes of the rollers so that the carriage is stable along the entire extent of its travel.The rack is secured to the flexure element with a single screw fastener whose axis is oriented perpendicular to the pinion axis.