The circumstances surrounding its introduction are as follows: In 1867 the Bridgeport Brass Company had a lot of sheet brass returned to them from the Union Metallic Cartridge Company as “out of gauge.” Investigation showed that the sheets were to the gauge of the manufacturer, but that the gauge used by the customer did not agree, and, further, when both gauges were tested by a third, no two of them agreed. All three gauges were supposed to be the regular U. S. Standard, adopted by the wire manufacturers in 1857, of the well-known round, flat form, with slits for the various sizes cut in the circumference. Gauges of this form were the best and most accurate method then known for measuring sheet metal. S. R. Wilmot, then superintendent of the Bridgeport Brass Company, seeing that the difficulty was likely to occur again, devised the micrometer shown at A in Fig. 44, and had six of them made by a skilled machinist named Hiram Driggs, under the direction of A. D. Laws, who was then in charge of the mechanical department of the Brass Company. The reading of the thousandths of an inch was given by a pointer and a spiral line of the same pitch as the screw, 40 to the inch, running around the cylinder and crossed by a set of 25 lateral, parallel lines. In the early part of 1867, the matter was taken up with J. R. Brown & Sharpe with a view to having them manufacture the gauges, and the one shown, A, Fig. 44, with Mr. Laws’ name stamped on it, is still in their possession. As submitted, the tool was not considered to be of commercial value, for the cylinder was completely covered with spiral and straight lines intersecting each other so closely that it was impossible to put any figures upon it, thus making it very difficult to read.