What is a Micrometer Used For?

Precision measurement tools are a vital part of making accurate and functional parts and maintaining the machines needed to do so. A micrometer is just one type, most commonly used by machinists, but it will often be found in the toolboxes of fabricators, engineers, and more.

In this article, we’ll look at what a Micrometer does, the different types, and how to use one.

What is a Micrometer Used For?

A Micrometer is used to precisely measure between two external faces, typically between 1” and 6”, although larger and smaller versions do exist. A micrometer can typically measure to a precision of 10 thousandths of an inch for imperial micrometers or 0.001mm for metric ones.

They are a commonly used tool by machinists and engineers and allow the accurate measuring of square, cylindrical and spherical parts.

Parts of a Micrometer

There are 7 main components to a micrometer:

• Frame, this holds the anvil and spindle concentric
• Ratchet stop, used to limit the torque applied when measuring
• Thimble, used to spin the micrometer open and show the whole units
• Sleeve, displays the vernier graduations of units
• Spindle, extends to measure the object
• Anvil, provides a hard and parallel surface

What Types of Micrometers Are Available?

Like most tools, there are specialized versions for different types of work, in the case of micrometers there are different types for measuring differently shaped objects:

Standard or Vernier Micrometer

This is the simplest and most common type of micrometer, it uses a vernier scale to accurately and quickly show the measurement. The benefits of standard micrometers are that they don’t require a battery and are typically cheaper than digital ones.

Digital Micrometer

As the name suggests, these have a digital LCD that indicates the measurement. They are often faster to read, especially for less-experienced users, and tend to have a higher level of precision.

Naturally, they are more expensive than a comparable standard micrometer and require periodic changes of the batteries.

Ball Micrometers

Instead of the flat surfaces on the anvils, ball micrometers have spherical ends, this allows for easier measurement of round parts, specifically involving internal diameters or radii.

Ball micrometers can be used to measure flat objects, but are more delicate and expensive than standard ones, so should ideally be kept for their intended use.

Thread Micrometer

Used for measuring threads, these have a point on the spindle and a double-v shape on the anvil, this allows them to index on the thread of a part. With some referencing to the appropriate tables, the thread’s pitch can be ascertained.

Internal or Bore Micrometer

These are used for measuring inside diameters, they lack the frame of the typical micrometer and instead have an anvil at each end. They are inserted into the ID to be measured and extended.

Depth Micrometer

Similar to the bore micrometer, a depth micrometer does not feature a traditional anvil and frame, instead there is a wide flange at the zero position. This allows the spindle to protrude into a hole, with the anvil resting on the top surface.

This allows for extremely precise measurement of depths, such as in holes, slots, rebates and grooves.

How to Use a Metric Micrometer?

First: Check the micrometer is not damaged or mis-adjusted. Wind the sleeve all the way to zero (use a gauge block if the lower end is not zero) and check the vernier graduations line up at zero – this helps to confirm the micrometer is properly set up.

1. Place the part in between the anvil and spindle, and wind the ratchet stop in, ensuring that the anvil face is parallel to the face of the object.
2. When the ratchet stop clicks, read the whole unit number, indicated by the bottom graduations of the sleeve measurement
3. Note if there are any half-mm graduations showing on top of the sleeve markings, if so add this to the whole-unit number
4. Finally, read the vernier scale on the thimble, add this to the numbers so far.

How to Maintain a Micrometer

Micrometers should be kept dry, and ideally at a consistent humidity and temperature, failing to do so can cause them to lose accuracy over time.

Oil the mechanism as described in the manual, and ensure if very accurate measurements are needed, you calibrate the micrometer against a gauge block periodically.

Are Micrometers Better than Calipers?

There are a few key differences between micrometers and calipers, typically the latter are used to measure larger items, with the minimum measurement range being 0-150mm, and 0-300mm being common too.

Calipers typically measure down to 0.02mm, which is many times less precise than a micrometer. Another disadvantage is the physicality of the tool too, whereas the micrometer places the object to be measured directly in line with the measuring scale, a caliper is offset.

Whilst this can be useful in certain situations, such as where a caliper can be easily used and a micrometer can’t, it can introduce inaccuracy, a perfect example of the Abbe principle.