How to Use a Micrometer

A micrometer also known as a micrometer screw gauge is a mechanical device that allows measurement of the size of an object.

It is widely used by mechanical engineers and machinists for its precision in measurement.

There are three common types of micrometers: outside micrometers used to measure wires, spheres, shafts, and blocks; inside micrometers used to measure diameters; and depth micrometers used for slots and steps.


  • The line on the sleeve marked “1” represents .100″, the line marked “2” represents .200″ and so forth. Each of these is further divided into four subdivisions of .025”.
  • The thimble is divided into twenty-five equal parts, each of these parts is equal to .001″, and a complete rotation of the thimble coincides with the smallest division (.025″) on the sleeve.
  • Place the object to be measured between the anvil and spindle. The anvil and spindle are in the form of a C-shape.
  • Turn the thimble until the spindle meets the object. To apply pressure to the object, turn the ratchet to close down and tighten the spindle.
  • Lock the thimble using the clamp ring
  • Read the markings on the sleeve and on the thimble: read the exposed number on the sleeve, and then read the number of divisions past the number. Read the division on the spindle.
  • Add the numbers to arrive at the measurement.


  • For accurate measurement use the friction screw or its equivalent to close the rods on an object.
  • Assign a margin of error; Plus/minus 0.003mm is recommended