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What is a Micrometer?

What is a Micrometer?

A micrometer is a precision measuring instrument, used to obtain very fine measurements and available in metric and imperial versions. Metric micrometers typically measure in 0.01mm increments and imperial versions in 0.001 inches.

The measurements they provide can be more accurate than those given by other measuring devices such as dial calipers or vernier calipers, but depend very much on the user’s care.

Measuring using Micrometers

They are widely used in mechanical engineering for precisely measuring components.


Micrometers have two scales: a primary scale, on the barrel or sleeve, and a secondary scale, on the thimble.


Values are taken from each of these scales and combined to make the total measurement. 

Some micrometers also have an additional vernier scale on the thimble, which provides the user with readings of even greater accuracy.


A micrometer uses a calibrated screw or thread (found internally on the spindle) for measurement.


Every time the spindle makes a complete revolution, the space between the measuring faces of the instrument (the spindle and the anvil) is adjusted by 0.5mm for metric versions and by 0.025 inches for imperial micrometers.

These are the smallest values that can be represented on the primary sleeve scale.


Although micrometers are highly accurate measuring devices, they are limited in their range.


Micrometers typically have a measuring range of 25mm and 1 inch. For instance, metric versions measure 0-25mm, 25-50mm, 50-75mm etc, and imperial versions measure 0-1 inches, 1-2 inches, 2-3 inches etc.

There a number of different types of micrometer.


The most common are the outside micrometers. Inside micrometers and depth micrometers are also widely available.


At Wonkee Donkee we have made a list of the best micrometers for different jobs.

Wonkee Donkee Tools