The sleeve _A_ is composed of the inside measuring disk, the graduated sleeve, and the micrometer nut combined. On the disk are two projections _KK_, which are knurled, thus providing a grip when operating the tool. The sleeve is threaded on the inside of one end, which acts as a micrometer nut, and the outside of this same end is threaded to receive the adjusting nut _D_. The sleeve has two slots, each placed 90 degrees from the graduations, and these provide for compensation for wear. The disk part is hardened by heating in a lead bath, and is finished by grinding and lapping. The barrel _B_ is the same as a regular micrometer barrel, and is graduated with 25 divisions. Spindle _E_ consists of the outside disk and the micrometer screw, and the barrel _B_ fits on its end, which is tapped out to receive the speeder _C_, which serves to hold the barrel in position. The thread is ¼ inch, 40 pitch, and the disk and unthreaded parts are hardened, ground and lapped. To adjust this, instrument, loosen the speeder _C_ and turn the barrel until the proper adjustment is obtained. Then lock the barrel by tightening the speeder again.[9] [Illustration: Fig. 20. Micrometer in Fig. 19 used as Height Gage] Micrometer Caliper Square Fig. 21 shows an assembled view and the details of a micrometer caliper square which, if accurately made, is equal and often preferable to the vernier caliper now so generally used. One of its advantages over the vernier is that when the measurement is taken, it can be readily discerned without straining the eyes, and this instrument is as easy to manipulate as the regular micrometer. In the details, part _A_, which is the main body of the instrument, is made of tool steel, the forward or jaw end being solid with the body. This end is hardened, and the jaw ground and lapped. The body is bored out and two flats milled on the outside, which lighten it up and make it neat in appearance. The jaw end is counterbored out with a 45-degree counterbore to form a bearing for the forward end of the micrometer screw. A slot, 1/8 inch in width, extends from the fixed jaw to the other end, and in this slides the movable jaw _C_. There are 44 divisions along the side of this slot, each division being 0.050 inch apart, giving the tool a range of 2.000 inches for outside and 2.200 inches for inside measurements. The screw _B_ is the most essential part of this tool, its construction requiring great accuracy. Its diameter is 3/8 inch and it is cut with 20 threads per inch. On its forward end fits the cone _F_, which is hardened and ground, the round part acting as the forward bearing of the screw and fitting in the 45-degree counterbored hole in the body _A_. On its other end fits the graduated barrel _D_ and also the speeder _G_. [Illustration: Fig. 21. Micrometer Caliper Square]