A micrometer (sometimes called micrometer screw gauge) is a precision measuring instrument, used to obtain very fine measurements and available in metric and imperial versions. They use a calibrated screw or thread (found internally on the spindle) for precise measurement of components in mechanical engineering and machining as well as most mechanical trades. They usually come in the form of callipers e.g. opposing ends joined by a frame. Learn how to calibrate and use micrometers correctly in our comprehensive micrometers guide.

What are Micrometers are composed of?

Here is a list of different components that make up a typical multimeter:

  • Frame - The C-shaped body that holds the anvil and barrel in constant relation to each other,
  • Anvil - The shiny part that the spindle moves toward, and that the sample rests against,
  • Sleeve/barrel/stock - The stationary round component with the linear scale on it, sometimes with vernier markings,
  • Locknut / lock-ring / thimble lock - The knurled component (or lever) that tightens to hold the spindle stationary,
  • Spindle - The shiny cylindrical component that the thimble causes to move toward the anvil,
  • Thimble - The component that turns by using a person’s thumb. Graduated markings,
  • Ratchet stop - Device on the end of the handle that limits applied pressure by slipping at a calibrated torque,
  • Screw.

How do they work?

The precision is determined by the thread pitch of the spindle. The spindle is a very accurately machined screw and the object to be measured is placed between the spindle and the anvil. The spindle is moved by turning the ratchet knob or thimble until the object to be measured is lightly touched by both the spindle and the anvil.

Types of Micrometers

  • Outside micrometer: most common type used to measure external dimensions such as the outside diameter of an object.
  • Inside micrometer; used to measure inside dimensions like the inside diameter of a hole or tube. There are two types: calliper-type and tubular and rod.
  • Depth micrometer: these are used to measure the depths of holes, slots and steps. They come with a variety of interchangeable rods of different lengths so that they can be used to measure a range of depths.


  • Provide very accurate measurements and are considered one of the most accurate types of measuring device
  • Ratchet speeder helps to provide reliable measurements
  • Integrated scales, the sleeve scale and thimble scale are built into the tool, another measuring instrument such as a ruler or tape measure is not required
  • Durability and long-lasting and unlikely to need replacing or repairing


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