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.


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


Outside Micrometers: Are industry standard measuring tools because of their high accuracy/resolution and ease of use. Mechanical OD micrometers are available in .001" and .0001" (0.01mm and 0.001mm) graduations. Electronic OD micrometers normally have .0001" or .00005" and 0.001mm resolutions. Standard OD micrometers are available up to 40"/1000mm. The accuracy of a micrometer is derived from several factors. The most significant factors are: thread accuracy, flatness of measuring faces, parallelism between the faces and rigidity of the frame which holds anvil and spindle. OD micrometers are available in a variety of different spindle and anvil configurations to allow the operator to measure difficult to reach features on a workpiece. The measuring range on a typical OD micrometer is 1" (25mm). Some special application micrometers have a smaller or greater range than 1" (25mm). Wide range OD micrometers (interchangeable anvil micrometers) are available and reduce the cost of a micrometer set, verses the cost of individual micrometers to cover the same range (typically a 6" range).