How to Read a Micrometer

How to Read a Micrometer

If you’re seeing the micrometer for the first time, then I believe you must be asking yourself “What on earth is this thing”. For those of you that are fans of Hollywood thriller movies, then you might confuse it with one of those torture tools used by serial killers to brutalize their victims. But, if you happen to ask any mechanical engineer, mechanist, or just someone working in a technical field, then they’ll tell you that a micrometer is one of the must-have tools in any engineer’s toolbox. So, whether it’s for curiosity or you’re just an intern looking to polish your mechanical engineering skills, learning how to read a micrometer is one way you can advance your career to the very top.

Now, at first glance, a micrometer looks like a complex tool with multiple calibrations on its moving parts. However, it’s due to these calibrations that make this tool so efficient in recording inner and outer measurements of varying objects. But, despite being so accurate, micrometers require a high level of understanding of their working principle. Due to this reason, this guide has readied an insightful piece of information that will help you learn how to read this engineering tool.


Why Consider a Micrometer?

There are many reasons why engineers consider micrometers over dial and vernier calipers. One of these reasons is the different variations of the micrometer that are available that allow you to take accurate measurements of either the internal or external diameter of an object. They can also measure the length and depth of an object provided it fits in between the anvil and the spindle.

Other than that, micrometers come in either standard or digital variants. They’re also classified according to the principle they use to record measurements such as metric and imperial. Lastly, micrometers are believed to be very accurate due to their ability to adhere to Abbe’s principle.

According to Abbe’s principle, for a measuring tool to perform accurately, the scale of the measuring instrument and the measurement target must be placed in a collinear fashion. Since the scale of the micrometer and the object being measured are positioned in collinear, then it’s believed to follow Abbe’s principle.

Therefore, by following Abbe’s principle, a micrometer is capable of taking accurate measurements of up to one ten thousandths of an inch. With that said, here are some real-life applications of a micrometer.

  • Measuring Tube Wall Thickness: If you wish to know the diameter of tiny tubes such as a bullet cartridge when loading gunpowder, then the micrometer is the perfect solution.
  • Paper Thickness: If you’re looking to measure the thickness of a piece of paper, then a micrometer, especially the digital model, is the best you can use. The reason why the digital mode is the best is that it doesn’t have a rotating spindle that can press the paper and alter the measurements.
  • Measuring Narrow Grooves: To measure the diameter of narrow grooves, such as those on bolts or screws, a micrometer, such as a blade micrometer, is the perfect tool to consider. The reason why a blade micrometer is the best is due to its measuring faces that resemble a blade. This allows them to fit on tight gaps such as grooves to record measurements.


Types of Micrometers

Now, a micrometer is a measuring tool that’s widely used in many working fields such as engineering, mechanics, machinery, laboratory, and construction. To make it easier for you to take measurements, this tool comes in different sub-divisions with the most common ones being the outside micrometer, inside micrometer, caliper-type micrometer, tubular micrometer, and depth micrometer.

So, with that in mind, this guide will now highlight parts of the micrometer before moving on to discuss how exactly you’re supposed to read a micrometer.

Parts of a Micrometer

For you to understand how a micrometer works, you must master its key components. By analyzing these components, you’ll get to understand how exactly you can use the tool the record measurements.

  • Frame: The frame is definitely the rigid point of the micrometer that holds the anvil and the barrel for accurate measurements.
  • Anvil: The anvil is a shiny cylindrical part that’s usually stationed on one side of the C-shaped frame. Its purpose is to hold the object being measured.
  • Spindle: This is a shiny cylindrical moving part that protrudes from the ratchet towards the anvil to offer more reinforcement when holding the object being measured.
  • Thimble: This is a rotating vernier scale that contains graduated markings which give you the measurements of the object being measured.
  • Sleeve: This part is used to indicate the linear scale which indicates the readings in mm.
  • Locking Nut: The locking nut is very helpful when taking measurements as it secures the spindle preventing it from any movement.


How to Take Measurements

Taking Measurements Using an Outside Micrometer

  • Step One: The first step of measuring an object using a micrometer is to clean the anvil and the spindle before you begin. This will help to clear any debris that might compromise the results. Also, confirm the zero mark on the thimble to ensure it’s lined up with the scale on the sleeve.
  • Step Two: Next, hold the object to be measured with one hand and place it in between the anvil and the spindle.
  • Step Three: Using the other free hand, twist the ratchet counterclockwise until the spindle presses the object firmly.
  • Step Four: Lastly, set the thimble lock to ensure the spindle is locked and won’t move in the process.


Taking Measurements Using an Inside Micrometer

  • Step One: If you’re taking internal measurements of a tube, a ring, or any other cylindrical object, then you’ll need to use a tubular micrometer. So, here, you’ll start by testing all the available extension rods to determine which one fits into the interior space precisely.
  • Step Two: Once you’ve found the perfect extension rod, attach it to the micrometer and turn the thimble until it reads zero.
  • Step Three: Lastly, insert the micrometer into the opening and turn the thimble using the ratchet speeder until it holds both sides of the cylindrical object.
  • Step Four: Lock the micrometer using the lock nut to prevent any movement when recording the measurements.


How to Read a Micrometer: A Complete Guide

Reading an Inch Micrometer

  • Step One:

The inch micrometer is designed with calibrations both on the sleeve and the spindle. The scale on the sleeve is measured in a one-hundred thousandth of an inch which is represented by 0.100 in decimal form.

Now, one turn of the thimble moves the spindle face away or towards the anvil at exactly 1/40” which is translated to 0.025”. This means that the distance between two shorter lines on the sleeves is 0.025 inches.

The thimble isn’t left out either. It also has its own calibration with each line representing one-thousandth of an inch or .001 in decimal form.

  • Step Two:

With that in mind, it’s now time to record your reading. Start by reading the whole number on the sleeve. Supposing its 5, then you’ll round it into one-hundred thousandth which will make it 500 thousandth or 0.500.

  • Step Three:

Next, count the number of lines that appear after the whole number, which in our case is 5. If the line is just 1, then multiple it by 0.025 (which is the distance between one line) to have something like 1 x 0.025” = 0.025”.

  • Step Four:

Lastly, record the corresponding marking on the thimble that’s at least underneath the line on the sleeve commonly known as the datum line. Let’s assume the reading was 28. Since the thimble represents one-thousandth of an inch, this reading will be read as 0.028.

  • Step Five:

So, by adding all these figures together, you’ll have 0.500 + 0.025 + 0.028 = 0.553 inches.


Reading a Metric Micrometer

  • Step One:

In this type of micrometer, there are two calibrations on the sleeve which are the top and bottom. The top calibration represents the millimeter reading while the bottom calibration represents half a millimeter reading.

The readings on the thimble go all the way to 50 with each line representing a hundredth of a millimeter which is 0.01mm in decimal form.

  • Step Two:

Now, to record your reading, you’ll start by reading the whole number first which in our case will be a 5.

  • Step Three:

Next, read the half-millimeter lines that are showing after the whole number. Supposing its one line, then it would be 0.5mm.

  • Step Four:

Lastly, take the reading on the thimble and multiply it by a hundredth. Assuming you had 33, then your thimble reading will be 33 x 0.01 = 0.33mm.

  • Step Five:

So, to find the precise diameter of whatever object you’re measuring, then you’ll have 5 + 0.5 + 0.33 = 5.83mm.



As you can see, a micrometer is a reliable tool that allows professionals in various occupations to take measurements of very tiny objects which larger measuring tools would struggle to take. But, to be a professional in recording these measurements, you need to understand the psychology behind this measuring tool and most importantly, you need to understand the anatomy of the micrometer scale.

Thankfully, this guide has offered you everything you need to know about the micrometer. So, whether you’re a beginner, an intern, or just a curious learner, then the information I’ve offered is enough to kick-start your new career.

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