What Is A Micrometer?

Those who are in any business where they work with small items that must be measured accurately have likely heard of a micrometer before. A micrometer is a measurement tool that is capable of accurately gauging diameter, thickness, and length of objects as small as one-thousandth of an inch. Anything that fits between the spindle and the anvil of the tool can be accurately measured. You can measure outside diameters, inside diameters and depths with the more commonly used devices.


Micrometers are most commonly found being used by mechanical engineers and those who work with machining applications, but they can also be useful to people in many other industries as well. However, people who work with machines use them most frequently because most mechanical objects contain components that are tiny and need to fit together perfectly in order for the object to function as it is intended.

Uses For a Micrometer

Micrometers actually come in several different forms; if a person needs to measure the thickness of a wire, then they will need to use an 'outside micrometer'. If someone needs to measure the distance inside of something, such as the diameter of a hole, then they will need to use an 'inside micrometer'. There are even 'bore micrometers' that can measure the cross section of a hole that doesn't have a perfectly circular shape. A tube micrometer can measure the thickness of tubes, and a depth micrometer can measure slot or step depth. There are also micrometers that have special attachments which can change their function and measurement capabilities instead of having to use multiple tools.

There are many workers who can make use of a micrometer for their projects. For example, a mechanic may use a micrometer to measure the size of a brake disc if they need to have a new one made and installed into a vehicle. An engineer may use a micrometer to measure the thickness of a wire that goes inside a machine they are working on so they can accurately replace the damaged part. Measurements gathered by a micrometer are so accurate that they can actually find the thickness of a sheet of paper or even a human hair, so they can be used in a wide variety of applications.

Parts of a Micrometer

Those who are interested in using a micrometer or believe they may need one for something they are working on need to be well aware of the different parts of the measurement tool. Understanding the parts and how they work together can help someone more accurately use the tool. Reading measurements from a micrometer is not like reading measurements on a standard foot-long ruler; it takes some practice and a bit of skill to be able to use a micrometer effectively and correctly.


The parts of a micrometer include:

  • Measuring faces: Anvil and Spindle
  • Sleeve scale
  • Base line
  • Main scale
  • Ratchet speeder
  • Lock nut
  • Thimble
  • Frame

The index line and thimble scale will be used to gather readings, which are both located where the thimble and frame meet. The thimble is turned to accommodate the size of the object being measured, and the readout will change accordingly as the dial spins. It's important to mention that micrometers are tools that get calibrated on a frequent basis and rely heavily on being accurate. If one of these tools gets dropped or jarred around in some way, it needs to be immediately recalibrated as the readouts are no longer going to be accurate. When measuring objects so small, accuracy is critical.

Advantages and Disadvantages of Using a Micrometer

There are many advantages and disadvantages of using a tool as accurate as a micrometer. For those who are thinking that they may need to utilize one, considering the pros and cons is very important.

Here are the advantages of using a micrometer:

  • Micrometers provide extremely accurate readings, all the way to .0001 of an inch.
  • The ratchet speeder on the tool ensures that even pressure is used on the thimble, thus ensuring accurate readouts that can be repeated several times.
  • Micrometers include both thimble and sleeve scales, so the need for a ruler or other type of measuring device is not necessary.
  • Anvil micrometers are an inexpensive way for those who need to take multiple ranges of measurements.
  • There is a wide variety of micrometers to choose from, which is great for those who have unique projects. All forms of the micrometers are durable and made with quality materials as well.

The disadvantages of using a micrometer are:

  • Micrometers have a maximum range of 25mm, which is not enough for some people's projects
  • If someone needs to purchase a large micrometer, it's usually quite expensive
  • Larger micrometers are more difficult to use and read accurately
  • If a micrometer user needs to complete several measuring tasks, they may need to use several different micrometer tools, which can be cumbersome and time-consuming
  • They must be constantly checked for calibration against a standard

How to Read a Micrometer

Reading a micrometer is not such an easy thing to do. In order to read a micrometer, a user must have an understanding of the thimble and sleeve. These two parts of a micrometer have numbers on them which will provide the reading a user is looking for.

Here are the basic steps to reading a micrometer:

  • The numbers on the sleeve are divided into quarters, and numbers on the sleeve will either be concealed or revealed based on the turning of the thimble.
  • The numbers on the thimble represent hundredths.
  • Adding the number from the sleeve with the number on the thimble when the item is successfully locked into the frame will provide the measurement.

For example, if the number on the thimble was showing 3 and at the quarter mark after it while the sleeve showed a number of 1, the measurement would be .326 inches. This is how the two numbers get added together to provide a reading on a micrometer.

All in all, a micrometer is a useful tool that can help people complete a number of tasks on a very small scale. When it comes to ensuring the correct sized holes are cut on the hull of an airplane, accuracy is absolutely critical, therefore a micrometer is necessary. However, before someone goes out and buys the first micrometer they come across, they would be wise to research the specific type they need and what sized tool they are going to need. It can be very easy for someone new to micrometers to purchase the wrong tool.