Last updated: September 3, 2021

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The micrometer is a measuring tool commonly used in mechanics-related work environments. It is the instrument used, for instance, to measure a screw or a vehicle's axle. You can also find micrometers designed to gauge the inside width of a nut or the depth of a specific part.

You can choose a model based on the different levels of accuracy it offers. The most basic micrometers are precise to one hundredth of a millimeter, while the most accurate can calculate lengths of one thousandth of a millimeter – in other words, one micron. In this article, we will tell you everything there is to know about these tools.

Key Facts

  • There are three basic types of micrometers, according to their use: inside, outside, and depth.
  • You can choose between analog or digital models.
  • Before you purchase a new micrometer, make sure that it comes with the measurement system – inches or millimeters – and range that you need.

Our Selection: The Best Micrometers

As we will discuss later, there are several types of micrometers on the market: inside, outside, and depth models. In addition, you can choose between the traditional mechanical tool or a digital product. In the following section, you will discover our very own selection of the best micrometers currently available out there.

Shopping Guide: Everything You Should Know About Micrometers

As you now know, micrometers can come in a variety of types and sizes. Designed to measure thickness and dimensions, the outside micrometer remains the most common. Let's now delve into what these tools are exactly and their main purposes. The information you will find in the section below will help you identify the right micrometer for your needs.

Hombre con micrómetro en mano

What a micrometer does is actually magnify the reading of very small lengths that would otherwise be extremely difficult to measure.
(Source: Kittiwut: 42066113/

What is a micrometer exactly?

Also called a micrometer screw gauge, this precision instrument is designed to measure the thickness and dimensions of various objects. It has two tips (jaws) that can be joined by a spindle with an engraved scale.
All you have to do is read the markings on the scale to obtain the measurement.

Some micrometers are accurate to one hundredth of a millimeter (0.01 mm). The more precise ones live up to their name and can measure down to a micron, or a thousandth of a millimeter (0.001 mm). You can find other tools that work similarly, such as the traditional Vernier caliper.

What are the different parts of a micrometer?

In the list below, you will learn more about the different elements that make up an outside micrometer. It is a compact tool, so its different parts are assembled to fulfill a specific mechanical function within the thickness measurement process.

  • Body. This consists of the arc and the frame of the micrometer. It usually has thermal insulation plates to prevent the material from expanding with the heat, which would affect its overall accuracy.
  • Anvil. It is the end of the micrometer against which the sample rests.
  • Spindle. This moving metal cylinder usually has its end hardened with a heavy-duty alloy.
  • Lock nut. This is the locking system that allows you to immobilize the spindle.
  • Sleeve, barrel, or stock. Attached to the body of the micrometer, this is the stationary part that contains a fixed scale (from 0 to 25 mm in the smallest tools).
  • Thimble. It moves at the same time as the spindle and features an engraved scale with 50 divisions.
  • Ratchet stop. Located at the end of the micrometer, it is designed to regulate the force that you will exert during the measurement.

micrómetro para trabajo

The working principle of operation of the micrometer is similar to that of a screw and nut.
(Source: Kittiwut: 34791515/

What are the primary uses of the micrometer?

As we mentioned previously, there are three different types of tools depending on the type of measurements you want to take: outside, inside, or depth. This last kind of micrometers is used to measure the depths of certain holes and slots. Here is a quick list of other practical applications:

  • Laboratory measurements
  • Automobile repair shops
  • Machinery calibration
  • Jewelry

On the other hand, the shape of the anvils determines other more specialized uses for high-precision measurements within the fields of mechanics and engineering. For example:

  • Plane parallel anvils. These are commonly used to make measurements of flat surfaces in parallel.
  • Conical anvils. They are designed to measure the space between the edges of a surface with a thread.
  • Disc-shaped anvils. They help calculate the space between the teeth of a gearbox.
  • Circular anvils. They are used to measure the diameter of small holes.

Piezas del micrómetro

The micrometer is one type of caliper.
(Source: Kittiwut: 94932516/

How does a micrometer work?

The working principle of operation of the micrometer is similar to that of a screw and nut. By turning the ratchet stop, you produce an axial movement that moves the screw by 50 hundredths for each full turn (360 degrees). This is why the thimble is engraved with a scale divided into 50 sections.

What the micrometer does is actually magnify the reading of very small lengths that would otherwise be extremely difficult to measure. To improve accuracy, subdivisions are included within the scale. This second scale allows you to fine-tune the measurement on the main scale.

What types of micrometers are there?

Just like the micrometer itself is one type of caliper, there are sub-categories for this tool. We classify them by their specific use and the reading display. Other instruments, such as the traditional vernier caliper, can fulfill the functions of the micrometer. You can find the different types below:

Type of measurement

  • Outside micrometer. Most frequently found in industrial environments, it is used for external measurements: spheres, screws, wires, axles, and mechanical parts in general.
  • Inside micrometer. Its role is to measure the diameter of spaces, such as bores or holes in the wall.
  • Depth micrometer. As its name suggests, it calculates the inner depth of a part.

Type of reading

  • Analog. This traditional micrometer has a mechanical operation.
  • Digital. These models have the same shape and function, but the reading comes in the form of digits on a screen.

Micrómetro de cerca

Traditional micrometers only work with one of the two measuring systems.
(Source: Kittiwut: 65715737/

What are the available micrometer sizes?

These tools have different sizes based on their measuring range. The most popular remains the 25-millimeter outside micrometer. This makes sense, as their most common application focuses on measuring small parts with the highest possible accuracy.

The 25-mm micrometer is found in any automobile repair shop, but there are other sizes that follow a pattern of 25 millimeters. This means that, if the smallest tool has a measuring capacity of up to 25 mm, subsequent sizes have a range of 50 mm, 75 mm, and so on.

How do I read my micrometer?

Simply add the values of the different micrometer scales. You will often have an additional 6-position Vernier scale to the nearest two thousandths of a millimeter, and an 11-position Vernier scale to the thousandth of a millimeter (0.001 mm). This is how it works:

  • One full turn of the thimble moves the screw half a millimeter (0.5 mm), which is the diameter of the micrometer screw.
  • The horizontal line on the handle features a scale graduated in millimeters. Each of these millimeters is divided into two below that line.
  • The beveled edge has 50 graduations. Each one represents one hundredth of a millimeter (0.01 mm). The number scheme on the scale appears in steps of 5 to facilitate the reading.
  • The most accurate micrometers include additional scales to measure hundredths (0.01) and even thousandths of a millimeter (0.001 mm).

Trabajador con micrómetro

If you use the metric system, be careful not to choose a micrometer with the scales graduated in inches.
(Source: Kittiwut: 28351373/

What is the difference between the micrometer and the vernier caliper?

The vernier caliper has been the most precise instrument for centuries. In fact, the micrometer adopted the Vernier scale to increase measurement accuracy. However, the micrometer screw gauge was invented by Jean Laurent Palmer in 1848.

If we had to summarize the main difference between the two tools, we could say that the micrometer gains in precision, while the caliper gains in versatility. Choosing either one depends on the specific measurements you need to make. We have compared the two instruments in the table below:

Micrometer Vernier caliper
Precision It can measure accurately to one hundredth of a millimeter (0.01 mm), or even to one thousandth of a millimeter (0.001 mm). It isn't as precise as the micrometer. Its minimum graduation is two hundredths of a millimeter (0.02 mm).
Ease of use The micrometer screw gauge doesn't require any special manual skills. This extremely delicate measuring instrument requires a certain amount of handling skill.
Durability Its robust construction guarantees flawless operation without deformation.
The measuring ends (the anvil and the spindle) are made from a particularly hard alloy to prevent wear.
You should avoid bending or scratching it.
Metal shavings must also be kept away, as they can get between the parts and damage the instrument.
Versatility Micrometers usually have one function: inside, outside, or depth. The vernier caliper can measure dimensions in all 3 variants.

Shopping Criteria

A micrometer isn't necessarily something we have in our toolbox at home. This specialized measuring instrument is most common in work environments, and repair shops or jewelry making are trades that require the kind of precision that a micrometer offers. Here are some criteria to keep in mind when making your purchase:

Degree of Precision

Micrometers are usually accurate to within one hundredth of a millimeter (0.01 mm) or the equivalent in inches (0.00005"). If you don't need that much precision, you can opt for a vernier caliper. On the other hand, you can also find models that go down to one thousandth of a millimeter (0.001 mm). Evaluate your needs before settling for a specific model.


How you use this tool is a fundamental criterion in your final decision. As you already know, you have the possibility to choose between three different types of micrometers depending on their functionality: inside, outside, or depth. Remember that the external measurement of thickness and dimensions is the most common task.

The most subtle differences also fall within the outside micrometer category. Keep in mind what we discussed earlier regarding the different anvil types – parallel, conical, or circular – used to measure flat surfaces, threaded surfaces, or gear teeth, for instance.

Size of the Measured Parts

We have already looked at the different micrometer sizes that follow a progressive pattern of 25 in 25 millimeters. You may require different sizes if you work in a garage. In any case, the most common one remains the 25-mm micrometer both in mechanics and other trades that need precision.

You can naturally use a 50-mm model to measure 25-mm parts, but the smaller version will be more comfortable to use. If your work involves measuring components with significant differences in size, your best option might just be the vernier caliper – provided that you can settle for a maximum accuracy of 0.02 mm.

micrometro con sus piezas elementales

The micrometer is a measuring tool commonly used in mechanics-related work environments.
(Source: Kittiwut: 34791514/

Digital or Analog

Mechanics professionals have been using the micrometer for decades now. Once you become skilled with the analog micrometer, you will tend to continue with this system. Standard micrometers are rugged and can withstand shocks better than any digital micrometer since they have no screens to be broken.

In our selection of products, you may have noticed that there is a wide variety of micrometers available on the market. Digital models integrate a backlit display to facilitate the reading in very bright environments. Besides, digital readers are capable of measuring in both millimeters and inches.

Measurement System

This is yet another essential factor that can lead to fatal errors if you neglect it during your purchase process. Indeed, if you use the metric system in your work, make sure that you don't choose a micrometer with the scales graduated in inches. Analog models will only feature one of the two measuring systems.

If you need both or want to avoid any potential confusion, choosing a digital micrometer will make all your worries disappear. This technology allows you to switch from millimeters to inches at the touch of a button. This type of micrometer saves you from converting units, which can be tedious and lead to measurement errors.


Not everyone has a micrometer in their toolbox. If you've come this far, you're probably a professional mechanic, a jeweler, or a DIY enthusiast. These tools will come in very handy whenever you need to measure the thickness of a screw or another small part. You now know exactly how they work and the different types available out there.

If you're thinking of buying a micrometer, make sure you consider the type of measurement you need to take: outside, inside, or depth. In addition, check that the tool uses the right measurement system: millimeters or inches. If you need both, a digital micrometer will perfectly do the trick.

If you found our shopping guide informative and useful, feel free to leave us a comment in the section below. You can also share this article on your social media!

(Source of featured image: Witsonkitiwutt: 65693790/