Micrometer: Types, Parts, Principle, How to Read (mm & inches)

Today you will learn types of micrometer, parts of micrometer, working principle of micrometer and at the last how to read a micrometer in mm and inches with an example.

So before knowing how to read a micrometer in mm and inches, First of all, we have to know what are these types, what are the parts of the micrometer, on which principle the micrometer works, Then we will be able to take micrometer readings with accurately.

On How to read a micrometer, You need to know about measuring technique, zero error, methods of removing zero error.

This is just a brief overview but we will know further in detail.

So let’s start step by step complete overview of a micrometer and then after know, how to read a micrometer in mm and inches.

What is a Micrometer?

A micrometer is a device that is used to measure dimensions of length, diameter, and thickness accurately.

Sometimes micrometer is also called a micrometer screw gauge.

Types of Micrometer

If we talk about the type of micrometer there are so many types of micrometer available in the market.

So here we only discuss that type of micrometer which is widely used in industries.

There are the following types of micrometers are widely used in industries:

  • Outside Micrometer
  • Inside Micrometer
  • Depth Micrometer
  • Screw Thread Micrometer 
  • Tube Micrometer 
  • Rolling Mill Micrometer
  • Electronic Micrometer 
  • Digital Micrometer

See in the figure different types of micrometers which are described below in detail.

types of micrometer
Different Types of Micrometer

Outside Micrometer

Outside Micrometer Used to measure external dimensions.

Like outside diameter of the shaft, flat plates thickness, etc.

Inside Micrometer

Inside micrometer is used to take direct measurement of internal sizes, such as the diameter of the holes, or the distance between two parallel surfaces.

The principle of measuring it is similar to an outside micrometer.

Measuring by an inside micrometer, its measuring surfaces are hard and grinded in rounding that allows for accurate measurement and when the instrument needs setting its movable jaw can be tightened.

Inside Micrometers, 25 mm to 50 mm and 50 mm to 150 mm are found to measure in the range, whose reading precision is 0.01 mm.

Depth Micrometer

It is used to measure the depth of holes, slots, projections, recesses, keyways, etc.

Its principle of functioning is similar to that of an outside micrometer.

Its design consists of a grinded and wrapped hard base, which is then recessed with a micrometer head.  

Screw Thread Micrometer 

This micrometer is used to measure the pitch diameter of a screw thread.

Its structure is similar to that of an outside micrometer.

Tube Micrometer 

This micrometer is used to measure the thickness of the walls of tubes, pipes, etc.  

Its anvil is spherical.

Rolling Mill Micrometer

This type of micrometer is designed primarily to check the thickness of the sheets when rolling so that the sheet ends are fixed away to measure.

But this micrometer is also used for other measurements where there is a need to take measurements in more depth.  

Electronic Micrometer 

This is a convenient instrument to use.  Measurements with a minimum count of microns (0.001 mm.) are used.

Its spindle opens with the help of a push-button and slides on the job.

The size of the measurement is displayed on a dial that can be read easily.

Micrometers of this type are made in different ranges. 

Digital Micrometer

A digital outside micrometer is a modern micrometer used for external dimensions of 0.001 mm used to measure in precision.

It has all the parts that are in a Vernier outside a micrometer.

Apart from this, it has a digital counter which is fixed on the frame and gives a direct numerical reading for quick and accurate measurement. 

Parts of Micrometer 

There are commonly various used micrometer is outside micrometer so here discussed outside micrometers part and also all types of micrometer parts are almost same.

There are following parts are used in the micrometer:
  • Frame
  • Anvil
  • Spindle
  • Sleeve
  • Thimble
  • Ratchet Stop
  • Spindle Lock Nut

See in the figure different parts of the micrometer which are described below in detail.

how to read a micrometer
Micrometer Parts

The outside micrometer has the following parts:


It is made from forged steel or malleable cast iron.

With this frame, all other parts of micrometers are attached.


Anvil about 3 mm is carried out on the frame.

It is one of the measuring ends.

It is made of alloy steel finished on a completely flat surface. 


The spindle moves and grips the job against the anvil.

So that it gets forward and backward movement.


It remains fixed on the frame.

Datum line and graduation are made on it.

It is also known as a barrel.


It is a tubular cover that is attached to the spindle and moves along the spindle.

There is a bevel edge on the thimble which is divided into 50 equal parts. 

Each 5th is numbered like 0, 5, 10, ... 45

Ratchet Stop 

This is the enlarged section on the thimble. This ensures uniform pressure between the measuring faces.

Spindle Lock Nut 

This is used to lock the spindle in a fixed position. 

Working Principle of Micrometer 

The micrometer works on the screw-nut principle.

During a round, the movement of the length of its spindle is equal to the pitch of the screw.

The movement of the spindle to the distance or part of the pitch can be accurately measured on the sleeve or barrel and the thimble.  

Metric micrometers have 0.5 mm pitch threads on the spindle.

Thus spindle 0.5 mm in one round of Thimble moves forward.

A 25 mm long datum line is formed on the sleeve or barrel.

The entire mm and half mm mark is made on this line.

The circumference of the Thimble and bevel edge is divided into 50 equal parts.

Therefore, the movement of a division of the thimble is 0.01 mm.

Thus, the Outside Micrometer has an Accuracy or Least Count of 0.01 mm.

How to Read a Micrometer in mm?

Finally, now we know step by step how to read a micrometer reading in mm.

Here we will learn to read the metric micrometer. 

Measuring Technique 

There are the following techniques taken to apply during reading a micrometer:
  1. Clean the face of a measuring micrometer with a soft cloth or paper.  
  2. Check the zero setting of the micrometer.  
  3. Hold the micrometer from the frame with the left hand and place the job between the anvil and the spindle.  
  4. Rotate the ratchet with the right hand and keep moving it until the sound of slip or rattle. 
  5. Ensure that the measuring axis is at right angles to the job axis and passes through the center. 
  6. Take Reading.

Micrometer Readings

To take readings from a micrometer, the following three items must be taken into consideration:
  1. Major divisions (the number of whole mm) 
  2. Minor divisions (number of halves mm)
  3. Thimble divisions (in front of the datum line)  

how to read a micrometer in mm
Micrometer Readings in mm

See in figure Lower line shows the major divisions which represent the whole millimeters of graduation.

The upper line shows minor division which always represents one-half millimeters graduation.

In front of the datum line shows thimble division.

Which is divided into 50 equal divisions and which reading shows in thimble division is multiplied by 0.01 mm. 

After then which reading is obtained? It will be thimble divisions readings.

During reading the Metric micrometer, First read the major division readings.

Then read minor division reading, if the additional line is shown in the minor division.

After that read thimble division reading and its multiply with 0.01 mm.

After that added these three values and which value obtained is a micrometer reading.

Refer to figure and clearly shown 

Major divisions readings: 38 mm

Minor division readings:  0.5 mm

Thimble division readings: 29  mm

Multiply with 0.01 mm then found reading is actual thimble division reading
0.29 mm

After that add these three values and then which final reading is obtained.
It will be a micrometer reading.

Micrometer readings – 38+0.5+0.29 = 38.79 mm

Note: Some micrometer manufacturers can reverse the position of full and half millimeters graduations and but The order in which you read the micrometers remains the same.

How to Read a Micrometer in inches?

The reading of micrometer in inches is the same as metric micrometer readings because all parts are the same but the only difference is in their graduation and least count.

The spindle of an inch-system micrometer has 40 threads per inch so that one turn moves the spindle axially by 0.025 inches, which is equal to the distance between two graduations on the frame.

The 25 graduations on the thimble allow a further division of 0.025 inches so that turning the thimble through one division moves the spindle 0.001" axially.

The rotating scale on the thimble represents a movement of 0.025" for each complete revolution. 

The line in the middle of the sleeve is used to line up the thimble readings.

Total Scale Reading  =  (MS + CS × LC)                           

MS = Main scale reading

CS = Circular Scale Reading

LC = Least Count

how to read micrometer in inches
Micrometer Reading in inches

See in the figure here

To find out Main Scale Reading, Adding the Major Division Reading to the Minor Division Reading.
 Main Scale Reading = 0.0500 + 0.075
                                     =  0.125"

Now show in the figure that the thimble division reading is obtained by multiplying the circular scale reading by the least count.


Thimble division reading = 7 × 0.001
                                             = 0.007"

As we know,

Total Scale Reading  =  (MS + CS × LC)   

                                      =  0.582"

So, 0.582" is a micrometer reading in inches.

Zero Error of a Micrometer 

Keep moving the micrometers until it touches the anvil.

If the zero of the thimble does not correspond to the datum line on the sleeve, then the micrometer is called a zero error.

If the micrometer gives a reading in plus, then it has a negative zero error.

This error is subtracted from the actual reading.  

If the micrometer gives a reading in minus then it has a positive zero error.

This error is added to the actual reading.  

Methods of Removing Zero Error

There are the following methods to given for removing zero error:
  1. By adjusting the sleeve of the micrometer with the help of a spanner available in the micrometer box.
  2. By adjusting the nut between the micrometer and thimble.
  3. In some types of micrometers, the anvil is fitted by a screw.  They are can be adjusted by screwing or unscrewing the anvil.

Test Pieces of Micrometer

These are round pieces of alloy steel that are hard and grinded in precision as per the range of micrometers such as 25 mm, 50 mm, and so on.

These peaces are used to check the micrometer and zero error.

The following are the reasons why micrometer readings are wrong:
  1. Wrong setting of zero line of Thimble. 
  2. Apply too much or too little pressure on the thimble.  
  3. Missing work.  
  4. Screw failure.  
  5. Micrometer frame twisted.  
  6. Deteriorating micrometer measuring face. 

Care and Maintenance

There are the following care and maintenance employed:
  1. Before taking the measurements, wipe the anvil and work and clean it thoroughly. 
  2. Do not apply excessive pressure while measuring. Often two clicks of a ratchet are sufficient. 
  3. When the micrometer is not being used, do not let its anvil faces in contact.
  4. The thread should be properly greased or oiled.
  5. Cotton waste should not be used while cleaning the micrometer.
  6. Do not place the micrometer on the bed of the machine, it may malfunction there.  
  7. When the micrometer is not in use, keep it in its box.  
  8. After a few months, the micrometers keep checking the accuracy.  

So friends here I discussed how to read a micrometer and also its types, parts and working principle, etc.

I hope you all clearly understand.

FAQ for Micrometer

Which part of the outside micrometer ensures a uniform pressure between the measuring surface?

Ratchet stop is the part of the outside micrometer which ensures a uniform pressure between the measuring surface.

To read a micrometer you first read the?

One should first read the main scale reading which is marked on the sleeve.

An outside micrometer has a negative error the correct reading can be taken by?

When the outside micrometer has a negative error, the correct reading can be obtained by adding the negative error to the actual reading.

How many divisions are graduated on thimble?

Micrometer thimbles have graduated 50 divisions with each division equal to 0.01 mm.

Which part is the measuring face fitted to the frame of the outside micrometer?

Anvil is the part of a micrometer fitted to the frame of an outside micrometer.

What is the use of a tube micrometer?

This micrometer is used to measure the thickness of the walls of tubes, pipes, etc.

Which type of micrometer is used to measure the exact depth of holes?

A depth micrometer is used to measure the exact depth of holes.

Which spanner is used for zero setting in an outside micrometer?

Mostly hook spanners are used for zero setting in outside micrometer.

What is zero error in a micrometer?

If the zero of the thimble does not correspond to the datum line on the sleeve, then the micrometer is called a zero error.

A digital micrometer is used to measure?

The Digital Outside Micrometer is a modern micrometer used for outside dimensions of 0.001 mm that are used to measure in precision.

What are the parts of a micrometer?

Frame, anvil, spindle, sleeve, thimble, ratchet stop, spindle, lock nut are the parts of a micrometer.

What are the different types of micrometers?

Outside micrometer, inside micrometer, depth micrometer, screw thread micrometer, tube micrometer, rolling mill micrometer, electronic micrometer, digital micrometer are the types of a micrometer.

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