Abstract From personal experience the author gives examples of progress made in reducing friction in sliding movements to a minimum, with the addition of preloading of the slide mechanism, so that higher operating speeds, greater precision of product, and longer life at lower cost are possible. Such preloading produces high stability in a slide because operating loads merely modify the total load, either increasing or decreasing it, in contrast with conventional slides in which the live load changes from no load to full load, and usually with no reversal of load permissible. Actually, from the standpoint of mechanics, preloaded slides constitute the introduction of couples into the system which are available to resist other couples such as those due to eccentric loads.