The micrometer is a precision measuring instrument, used by engineers. Each revolution of the rachet moves the spindle face 0.5mm towards the anvil face. The object to be measured is placed between the anvil face and the spindle face. The rachet is turned clockwise until the object is ‘trapped’ between these two surfaces and the rachet makes a ‘clicking’ noise. This means that the rachet cannot be tightened any more and the measurement can be read.

micrometer

Using the first example seen below:

  1. Read the scale on the sleeve. The example clearly shows12 mm divisions.
  2. Still reading the scale on the sleeve, a further ½ mm (0.5) measurement can be seen on the bottom half of the scale. The measurement now reads 12.5mm.
  3. Finally, the thimble scale shows 16 full divisions (these are hundredths of a mm).

The final measurement is 12.5mm + 0.16mm = 12.66

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Types of micrometer

Generally, there are three types of micrometers commonly used, the outside(External) micrometer caliper( including the screw thread micrometer), the inside (internal)micrometer, and the depth(depth) micrometer. The outside micrometer is used for measuring outside dimensions , such as the diameter of a piece of round stock. The screw thread micrometer is used to determine the pitch diameter of screws. The inside micrometer is used for measuring inside dimensions , as for example , the inside diameter of a tube or hole, the bore of a cylinder , or the width of a recess .The depth micrometer is used for measuring the depth of holes or recesses.
Other types of micrometers are:
·Blade micrometer
·Disc micrometer
·Tube micrometer
·Screw thread micrometer
·Taper micrometer