In steam injector work, accurately ground reamers of unusual tapers are commonly required, and the gage shown in Fig. 47 was designed to maintain the prevailing standard. It consists of a graduated bar, 1 inch square, with the slot _F_ running its entire length. The stationary head _A_ is secured in position flush with the end of the bar, and the sliding head _B_ is fitted with a tongue which guides it in the slot. This head may be secured in any desired position by means of a knurled thumb nut. The bushings _D_ and _D'_ are made of tool steel, hardened and ground to a knife edge on the inside flush with the face. All bushings are made interchangeable as to outside diameter. The head _B_ is fitted with an indicating edge _E_ which is set flush with the knife edge of the bushing. The reading indicates to 0.010 inch the distance the bushings are from each other, and the difference in their diameter being known, it is easy to compute the taper. With this gage it is possible to maintain the standard tapers perfectly correct, each reamer being marked with the reading as shown by the scale.[25] Inside and Outside Adjustable Gages [Illustration: Fig. 48. Adjustable Gage for Inside and Outside Measurements] Fig. 48 shows an inside and an outside adjustable gage for accurate work, used in laying out drill jigs, and in setting tools on lathes, shapers, planers, and milling machines. The outside gage is shown in the side view and in the sectional end view marked _Y_. At _X_ in the same figure is a sectional end view showing how the gage is constructed for inside work. The top and bottom edges are rounded, so that the diameters of holes may be easily measured.