Have you ever needed to make an extremely precise measurement? Industries that work with small parts and fittings have to make precise measurements. In many places, the measurement should be close to the exact value to avoid potential danger. To obtain such precise and accurate measurements, we turn to micrometers.

What is Micrometer?

A micrometer is an instrument used for making precise linear measurements of dimensions such as diameter, thickness, and lengths of solid bodies. It is made of a C-shaped frame with a movable jaw operated by an integral screw. The fineness of the measurement depends on the lead of the screw while the accuracy of the measurement depends on the accuracy of the screw-nut combination.

It is often misunderstood with the micrometer (μm) – the standard unit of length measurement. Another common name used for a micrometer is micrometer caliper due to its similar appearance to the caliper.

Parts of a Micrometer

A micrometer is composed of the following parts:

  • Frame – It is the C-shaped body that holds the anvil and barrel in constant relation to each other. The frame is heavy and has high thermal mass. To prevent substantial heating up, it is covered by insulating plastic.
  • Anvil – The shiny part the spindle moves toward and the sample rests against.
  • Barrel – Stationary round component with a linear scale on it.
  • Screw ­– Found inside the barrel and is considered the heart of the micrometer.
  • Locknut – Component that one can tighten to hold the spindle stationary.
  • Spindle – Shiny cylindrical component that causes the thimble to move toward the anvil.
  • Ratchet Stop – The device on the end of the handle that limits applied pressure by slipping at a calibrated torque.

Heart of the micrometer

In a micrometer, the screw located within the barrel is considered the heart of the micrometer. The accuracy of the thread form of the screw determines the accuracy of the measurement. The screw’s thread is simply the ridges felt when touching a screw. The thread is the helical structure moving up the screw, converting torque to linear force.

Operating Principle of Micrometer

Micrometers transform small distances into large rotations of the screw that can be read from a scale. The basic operating principle of a micrometer are as follows:

  • The amount of rotation of an accurately made screw can be directly and precisely correlated to a certain amount of axial movement (and vice versa), through the constant known as the screw’s lead. A screw’s lead is the distance it moves forward axially with one complete turn (360°).
  • With an appropriate lead and major diameter of the screw, a given amount of axial movement will be amplified in the resulting circumferential movement.

When is a Micrometer Used?

A micrometer is used when the precise measurement is needed. Following is a list of applications of micrometer:

  • Machines with moving parts – Parts that move in and out of each other such as the piston need to remain in a steady straight line, otherwise, the slightest bit of sway can lead to faults.
  • Bearings and pipe fittings need precise measurements for their optimal functioning.
  • Micrometers are a preferred tool for measurement of the thickness of items such as metals.


Test your Knowledge on Micrometer

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