Abstract: This application relates to a device which is mounted onto a threadless shaft and which converts the rotary motion of the shaft into linear translation of the device. The device includes two blocks which have an axial bore therethrough and a plurality of roller bearings, four of which are disposed on the block called the adjusting block and two of which are disposed on the block called the mounting block. The adjusting block carries the tensioning devices which generate the friction between the bearings and the shaft. The mounting block is the component to which both the driven load and the adjusting block are secured. Pins are provided so that the blocks will always be assembled in the same orientation as they were when they were machined.