A depth micrometer is a measuring device that determines the depth of items such as holes. These tools are useful when drilling screw and bolt holes so that the hole does not go deeper than the screw. The basic use of a depth micrometer is not difficult but it can take some practice to learn how to read the device's measurements. Depth micrometers are available in a variety of rod diameters to fit different sized holes.
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Things you need
Wipe off the top of the object that you are measuring with a cloth to remove all dirt and debris. The surface must be clean so as not to interfere with the measurement.
Place the depth micrometer on a flat surface and turn the centre section, called the thimble, counter clockwise to retract the bottom rod until it is flat with the bottom of the micrometer. The measurement mark at the bottom of the thimble should point to "0."
Insert the lower rod of the micrometer into the screw hole and position it as far against one of the sides as possible. Turn the thimble clockwise to lower the rod into the hole until you feel the rod stop.
Remove the micrometer from the hole and hold it horizontally. Locate the number on the horizontal scale that meets the bottom of the thimble. Each line represents 1 mm, so if the thimble ends two marks after the number 10 the reading would be 12 mm. Make a note of the measurement.
Tilt the depth micrometer vertically and identify the number on the bottom of the thimble that meets the centre of the horizontal measurement scale. For example, if it aligns at one mark above the 15, it would measure 16 mm.
Add the first measurement to the second measurement to arrive at the total depth of the hole. Using the above example, you would add 12 mm to 16 mm to get a total hole depth of 28 mm.
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