# Micrometer (Screw Gauge): Working Principle, Least Count, Parts and Units

The micrometer is also known as the micrometer screw gauge and is used to measure the dimensions particularly linear dimensions of the objects. It is used to measure the outside diameter, thickness, and length of solid objects.

## Parts of the Micrometer

First of all, we will check the parts of the micrometer and will understand the function of each part. The micrometer has the following parts:

### Anvil

An anvil is a stationary part that is fixed with the frame and it is on the left-hand side when you hold the micrometer in your hand. Whenever you placed an object to measure the dimensions, it is kept against the anvil, and the spindle moves towards the job to get the measurement.

### Spindle

The spindle is a rotating part that is just opposite the anvil and the job is placed in-between the anvil and spindle. When we rotate the Rachet then it is the spindle that moves in or out to get the dimensions of the object. We can also say that it is the cylindrical component of the micrometer and it moves when we rotate the thimble.

### Frame

The frame of the micrometer is a ‘C’ shaped body that holds the anvil and the barrel in constant relation with each other. The frame is heavy and it is having a thermal mass. It is generally covered with insulating plastic plates that help to reduce heat transfer.

### Barrel

A barrel is a stationary round component in the micrometer having a linear scale on it.

### Thimble

The thimble is used to rotate the rotating scale over the main scale.

### Rachet

Rajat is a device that is on the end of the handle of the micrometer that limits applied pressure by sleeping at calibrated torque.

## Range of micrometer

A micrometer generally comes in the range of 0-25, 25-30, and 0-50 mm. However, the maximum range of the micrometer is limited to 500 mm.

## How to Read The Micrometer

Now, let us understand how we read the micrometer.

First of all, we need to verify the ‘0’th mark on the thimble should coincide with the ‘0’th division on the sleeve when the anvil and spindle both are brought together. The locknut enables the locking of the spindle when we take a reading and the ratchet ensures a feel that while taking a reading accessive force on the job is prohibited.

The graduations on the sleeve are given in the millimeters and it is called the main scale. Suppose if the smallest division on this main scale reads 0.5 mm then each revolution of the sleeve will advance the spindle face by 0.5 mm. And then suppose there is the number of divisions on the symbol which is 50, then the least count of the micrometer is .5/50 and that is .01mm.

Now, look at the example given below.

The main scale reading is 8.5 mm which immediately precedes the position of the thimble on the main scale. Now the least count of the instrument is 0.01 mm and the 22nd division of the thimble is coinciding with the main scale then the reading will be

8.5 + 22(0.01)mm = 8.72mm

## Types of micrometers

There are many types of micrometers that are used in industries or colleges and in schools.

• Disk micrometer
• Dial micrometer
• Universal micrometer

### What is the Least Count of Micrometer?

The least count of micrometer is .01mm.

### What is the Micrometer least count formula?

For this what you have to do is divide the Smallest division by a number of divisions.
Example for micrometer least count can be calculated by the below formula i.e;
= Pitch((least division value)/ number of divisions on the scale.
= 1/100 = 0.01mm
So least count of a Micrometer isĀ 0.01mm

### What are micrometers used for?

The micrometer is used to measure the dimensions, particularly the linear dimensions of the objects. It is used to measure the outside diameter, thickness, and length of solid objects.