Using a Micrometer
- A micrometer, or a micrometer screw gauge, is a tool used for measuring small widths, thicknesses or diameters
- For example, the diameter of a copper wire
- It has a resolution of 0.01 mm
- The micrometer is made up of two scales:
- The main scale - this is on the sleeve (sometimes called the barrel)
- The thimble scale - this is a rotating scale on the thimble
Components of a micrometer
- The spindle and anvil are clamped around the object being measured by rotating the ratchet
- This should be tight enough so the object does not fall out but not so tight that it is deformed
- Never tighten the spindle using the barrel, only using the ratchet. This will reduce the chances of overtightening and zero errors
- The value measured from the micrometer is read where the thimble scale aligns with the main scale
- This should always be recorded to 2 decimal places (e.g. 1.40 mm not just 1.4 mm)
The micrometer reading is read when the thimble scale aligns with the main scale
Examiner Tip
The most common mistake in exam answers when reading from a micrometer is not giving the reading to the correct number of significant figures! For a micrometer, this is always 3 significant figures. This is especially important for values such as '2.30 mm' where the 0 must be on the end to make it 3 sf instead of just 2 s.f (which would be 2.3 mm).
