Depth Micrometer

Figure 2-28.—Inside micrometer set. The 0.500 spacing piece is used between the spindle and the micrometer head so the range of the micrometer can be extended. A knurled extension handle is usually furnished for obtaining measurements in hard-to-reach locations. Reading the inside micrometer. To read the inside micrometer, read the micrometer head exactly as you would an outside micrometer, then add the micrometer reading to the rod length (including spacing collar, when installed) to obtain the total measurement. Depth Micrometer The depth micrometer is used to measure the precise depths of holes, grooves, and recesses by using interchangeable rods to accommodate different depth measurements (fig. 2-21). When using a depth micrometer, you must make sure the base of the micrometer has a flat, smooth surface to rest on and that it is held firmly in place to ensure an accurate measurement (fig. 2-29). Reading a depth micrometer. When reading a depth micrometer, you will notice that the graduations on the sleeve are numbered in the opposite direction of those on an outside or inside micrometer. When you are reading a depth micrometer, the distance to be measured is the value that is covered by the thimble. See figure 2-30; consider the reading shown. The thimble edge is between the numbers 4 and 5. This shows a value of at least 0.400 inch on the sleeve’s major divisions. The thimble also covers the first minor division on the sleeve; this has a value of 0.025 inch. The value shown on the thimble circumference scale is 0.010 inch. Adding these three values together results in a total of 0.435 inch, or the total distance that the end of the extension rod has traveled from the base. This measurement added to the length of the extension rod Figure 2-29.—Using a depth micrometer. 2-11