Inside Micrometer & Least count

Inside Micrometer is used to measure the larger internal dimension. Inside Micrometer can measure internal Diameter of holes and registers.

inside micrometer
Mitutoyo’s Inside Micrometer

Types of Micrometer

There are various types of micrometers available in the industry each used for a specific purpose. One such micrometer is the “Inside Micrometer”.The inside micrometer is used to measure the inner diameter of objects that are bonded by walls,cylindrical bore or hollow pipe.There are two types of Inside Micrometer

  1. Analog type Inside Micrometer
  2. Digital type Inside Micrometer

The least count is 0.01 mm for analog type and 0.001 mm for digital type.

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It can be measured by mm or inches and gives precise readings. The inside micrometers are also available in different designs and sizes for various measurements.

digital inside micrometer

The general equipment comprises of a measuring head or a micrometer unit; extension rods; spacer or spacing collar and a handle.

The measuring head consists of a thimble, which has one way marking and holds readings up to 50 mm which is the thimble division(TD) reading.

The sleeve or barrel have the main or index scale and sub-scales, they have two waymarking. The main scale can measure up to 25 mm and the measured value is known as MSD(main scale division).

On the frontier end of the measuring head which is also known as the anvil is a hole through which the extension rods are inserted to the inside micrometer. On one side of the anvil is a locking screw that is used to adjust the extension rods and holds it firm. On the other side, there is a hole that is used to fit the handle.

The handle is used to insert the inside micrometer through objects having depth. The posterior end also contains a screw that is used to adjust the thimble.

Range of inside Micrometer

Good quality steel is used in measuring head and spindle, but for the faces-high graded tool steel is used. The least count of the inside micrometer is 0.01 mm. The extension rods can be of different sizes ranging from 50 mm- 200mm, depending on the requirement.

inside micrometer 50-150
MItutoyo’s Micrometer

The extension rods are classified as

  • 50-75mm;
  • 75-100mm;
  • 100-125mm;
  • 125-150mm;
  • 150-175mm;
  • 175-200mm

.Extension rods are used for extensive objects having large diameters, it is used along with the spacer. The spacer is used for smaller diameter in addition to the measuring head. The spacer is of 12 mm.

How to measure inner diameter with Inside Micrometer?

The design of inside micrometers can also have jaws where one end is fixed and the other is movable.The working of inside micrometer is very simple.It basically consists of three steps

  1. fixing the rod and spacer
  2. adjusting the screw and
  3. measuring.

Its working same as analog type micrometer you can check here: External Micrometer

Precise readings are necessary to prevent faulty readings and leakages that can cause errors.

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