The silicones studied were found to fall into two main groups. One group, of which the dimethyl silicone was representative, exhibited high friction and severe wear on hard metals but low friction and slight wear on soft metals. The other group, which consisted of fluorinated silicones, lubricated all metals satisfactorily. This pattern of behavior was independent of chemical reactivity of the metal, and there was no evidence of physiochemical interaction between the metal and the lubricants examined. A dimensional analysis suggests that even under the conditions of high pressure and low speeds effective lubrication is provided by the fluorinated silicones because of their favorable pressure-viscosity characteristic.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Washington, D.C., October 13–16, 1964.