Uniform circular into uniform rectilinear motion ; used in spooling-frames forleading or guiding the thread on to the spools. The roller is divided into two parts, each having a fine screw thread cut upon it, one a right and the other a left hand screw. The spindle parallel with the roller has arms which carry two half-nuts, fitted to the screws, one over and the other under the roller. When one half-nut is in, the other is out of gear. By pressing the lever to the right or left, the rod is made to traverse in either direction.