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Light Industrial     Clerical/Professional     Human Resources     3/9/2010 7:31:25 PM
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Using a Micrometer

Pictured above is an "outside micrometer". This is a tool often used in manufacturing environments to make precision measurements of the outside dimensions of a piece. Let's take a look at some of the parts of this instrument:

Note that the distance measured is the distance between the spindle and the anvil. The piece is inserted here, and the spindle length is adjusted so that the piece being measured just touches the anvil and the spindle.
The thimble is rotated to increase or decrease the distance between the spindle and anvil, and the measurement is read from numbers printed on the barrel and the bevel of the thimble.


Now that we know what the different parts are, and how they are used, all we need to know is how to read the measurements. Although micrometers come in different sizes, they are all read in the same way. The example we will look at measures from 0 to 1 inch, with an accuracy of 1/1000 of an inch.


Above is a close-up of the barrel and thimble. To get the correct reading, we need to get 3 different measurements, and add them together.
  1. First, we need to determine how many major divisions are showing on the barrel. In this example, there are 5 because the "5" mark is the greatest whole number which the thimble is not covering. On this micrometer, each of these marks is equal to 1/10 of an inch, or ".100" Thus, our first reading is ".500"
  2. Next, we need to check how many minor divisions are showing after the last whole number on the barrel. In this case there are 3 marks after the number "5". Each of these marks measure 25/1000 of an inch, or ".025" Thus, our second reading is ".075"
  3. The third step is to read the thimble. Here we are looking for the mark that most closely lines up with the center line. As you can see, the mark that lines up with the center line corresponds with the number "12" (two marks above the 10). Each of these divisions is equal to 1/1000 of an inch, or ".001" Thus, our third reading is ".012"
  4. Lastly, we need to add the three readings together. In this case that would be:
    .500 + .075 + .012 = .587