We do not think it necessary to write at length on the advantages of this improvement, nor print our files of recommendatory letters. The necessity among intelligent millers and mill-owners for a good and durable self-tramming driving iron is already well established. Many attempts have been made to devise something for the purpose, and the results are numerous; among them the “slip driver,” and those with loose oscillating appendages for the weight of the stone to rest upon and be driven by, and when adapted to their work, imperfectly accomplish the design; their lack of durability, the obstruction presented to the free passage of grain or middlings to be ground, and the fact that their form does not admit of a free adjustment while driving the stone are the chief objections. It has been established that these faults are entirely avoided by the improvement illustrated in the accompanying cut, in which Fig. 1 is an elevation showing the iron ready to be cemented in the eye of the runner. Fig. 2 is a view of the bottom and inside, with the sockets for the reception of the ends of the driver. Fig. 3 is a sectional elevation of all the parts, including the spindle and driver. The bridge S S, in which the steel cock-eye is placed, is in the form of an inverted arch, and is a portion of the entire outside part. Being in this shape, it has the double advantage of increased strength, and, by the attachment above the point where the grain is distributed, making no obstruction whatever to the passage of the grain or other substance to be ground. The bearings for the ends of the driver, C C, are cast on the adjustable section of the iron shown on the inner part of Fig. 2. This being adjustable on the steel pins shown as passing through the lugs A A, gives to the ends of the driver at all times a free and equal bearing in a lateral direction. The object gained by this arrangement is the application of power by the driver to the inner section in a direct plane, parallel to the face of the runner stone, said plane at the same time passing through the cock-eye--hence there is no tendency whatever to tip the stone. When the ordinary spindle with stiff driver is put in tram to the face of the runner, the miller has no assurance that it will remain so, the chances, indeed, being constantly against it. The heaviest spindle is liable to spring from its true position by the pressure of the gear or belt in driving it; the face of the runner stone changes, and the best driver, or its bearings, will from unequal wearing of the metal or in other ways cause it to get out of tram. The results are uneven grinding, inferior flour and diminished yield. The trouble necessary to take the spindle out, turn over the runner, make a staff and file the ends of the driver, is generally sufficient to deter the miller from performing the disagreeable job, and the bad grinding is conveniently attributed to some other difficulty.