Micrometer Screw Gauge

The micrometer screw gauge (commonly shortened to micrometer) can measure lengths to accuracy up to 0.001 cm or 0.01 mm. This instrument is used to measure very short lengths such as the diameter of a thin wire or the thickness of paper.


The micrometer has two scales: the main scale on the sleeve and the circular scale on the thimble. One complete turn of the thimble moves the spindle by 0.50 mm. There are 50 divisions on the thimble.
Hence each division represents a distance of (0.50 ÷ 50)

mm = 0.01 mm.  

A micrometer therefore allows us to measure accurately up to 0.01 mm.

Method of Reading: 
- Read the main scale reading at the edge of the thimble. 
- Next, take the thimble reading opposite the datum line of the main scale. 
- The reading is found by adding the main scale reading to the thimble reading. 

TAKE NOTE---->

The screw should never be tightened too much. As such, the micrometers are fitted with a ratchet to avoid this, but in older models it is possible to damage the screw by over tightening.  

It is also a good experimental technique to clean the ends of the anvil and spindle before making a measurement. Any dirt on either of these surfaces could affect the reading. As this measures stuff as precise as 0.01mm, and the dirt is something like this length, so it would affect the accuracy of the experiment no matter what.