11 Types of Micrometers – Advanced Metrologist Guide!
Types of micrometers. Knowing the type of micrometer you need for your application is essential when using these precision measuring instruments. Here, we look at the main micrometer types, describing their functions and suitability for different uses.
However, before we get into the different types, let’s recap what a micrometer is:
What is a Micrometer?
A precision measurement tool, a micrometer can measure the width, length, or depth of any item that will fit in-between its spindle and anvil, or the anvil and spindle will fit inside it, such as a gap or groove.
Parts of a Micrometer
Features to look for in a Digital Micrometer
- Type of ratchet – The ratchet allows the user to move the spindle onto the surface of the item being measured, controlling the amount of force that is applied to it. There are two types of ratchet, ratchet thimble & friction thimble, which use different internal mechanisms. The friction thimble provides a smoother motion but is harder to operate, while the ratchet thimble turns round with clicks but is easier to control and more suited to the novice operator.
- Ratchet stop – The ratchet stop is located at the end of the thimble cap and is used to maintain equal pressure throughout the micrometers range
- IP rating – IP rating is the ingress protection your device offers. IP rated electrical devices have a number that tells you the amount of protection the device offers. IP54, IP65, and IP67 are commonly found on micrometers, read more about IP ratings here.
- Measuring surface type/tip type – The type of measuring surfaces on the anvil and spindle can affect the suitability for a specific use, and the durability and accuracy of the digital micrometer.
- Accuracy – The accuracy of a micrometer details the margin of error it will measure within, offering insurance that your measurements will be within the stated margin. This means the given measurement may be both above or below the actual length of the item being measured, this will be shown with a ± symbol. Accuracy is checked using gauge blocks and determines to what tolerance it can read the gauge block. For example, if you have a 25mm gauge block, a micrometer that has an accuracy of ±0.002mm would read the gauge block giving a maximum error of 0.002mm, above or below 25mm.
- Resolution – Is the smallest unit or change in size the micrometer will register. Most commonly, this is 0.001mm on current models, and sufficient for most applications.
- Repeatability – This is the deviation you can expect when an object is measured more than once under the same conditions by the same person using the same measuring method.
- Parallelism – Determines how parallel the measuring faces are to each other.
- Flatness – The flatness will determine how flat the anvil is to the micron level. Not all micrometers will have the flatness stated, which means it is unspecified. However, not knowing the flatness could lead to a margin of error when taking measurements across devices.
- Data Output – Data output is especially useful if you are taking a lot of measurements at one time. This is because any device with data output can store every measurement that is being taken, where you can access it later on. Some devices will go as far as populating a spreadsheet from a live feed.
11 Types of Micrometer
The size, design, and shape of the anvils are one feature that determines the micrometer type. Other design variations to the structure of the micrometer allow for use on specific applications; these could include a larger or different shaped frame.
There are many different types of micrometer. In this article, we’ll look specifically at 11 commonly used types.
Each of the 11 types of micrometer is designed for a specific application/s, choosing the correct micrometer will affect its suitability for its intended use and ability to provide accurate readings.
- Standard Micrometer
- Blade Micrometer
- Point Micrometer
- Universal/Multi-Anvil Micrometer
- Internal Micrometer
- Depth Micrometer
- Tube Micrometer
- Non-rotating Spindle Micrometer
- Sheet Material Micrometer
- Disc Micrometer
- Snap Micrometer
In this article, we will go over the 11 main types of micrometer in detail… Let’s get started!
1. Standard Micrometer
A standard micrometer (sometimes known as a micrometer screw gauge), is a handheld device that is widely used in mechanical engineering and machining for measuring a range of objects with extreme precision.
Standard micrometers can measure the external measurements of any object that fits in-between its anvil and spindle. Micrometers typically read to a resolution of 0.001mm (0.00005″), a degree of precision suitable for most applications, although some models offer resolution as high as 0.0001mm!
2. Blade Micrometer
A blade micrometer is a precision measuring device that has a blade-shaped anvil and spindle. This allows measuring of components where the standard micrometer measuring surfaces can’t reach. The blade-shaped anvils can access narrow recesses, with the blades easily slotting into ridges and grooves, making them perfect for measuring the diameter of fine shafts and key ways.
A common issue with lesser models of this type of micrometer is that the anvil and spindle do not align properly. To avoid this issue it is best to research models properly before making a purchase, we recommend global brands such as Mitutoyo, DML, Moore and Wright, Tesa & Sylvac.
3. Point Micrometer
A point micrometer is a precision measuring device with a pointed anvil and spindle. In fact, the end of the anvil and spindle have a flat tip, a small radius flat. This ensures accurate alignment and placement of the measuring faces on the surface of the item being measured.
An alternative to the blade micrometer, the finer pointed surfaces can reach into smaller recesses, grooves and holes where the dimensions of the point will not restrict your access.
Inaccuracies can occur in lesser models if the alignment of the anvil and spindle is not true.
4. Universal/Multi-Anvil Micrometer
Universal micrometers are precision measuring devices that have interchangeable anvils/measuring faces. This means you can swap the anvil and spindle from flat, blade, point, spherical, spline, disk, and knife-edge. The term universal micrometer is also a type of micrometer whose frame has modular components. This allows a micrometer to function as a depth mic, outside mic and step mic.
The universal micrometer is considered as a one-tool solution for its multi-application based functionality. These are ideal for someone who frequently measures a number of components that vary in size, shape, surface texture, and structure.
5. Internal Micrometer
An Internal micrometer (also known as an inside micrometer) is a precision measuring device that has protruding arms designed for measuring the internal dimensions of an object, an example being the diameter of a keyhole.
6. Depth Micrometer
A depth micrometer is used to measure the depth of bores and small holes. The depth micrometer has a base that rests across the top of the recess while the measuring rod measures the depth of the hole.
User experience and technique is important when using a depth micrometer to ensure accuracy. As with all precision measuring instruments, care must be taken to achieve accurate readings. A delicate touch is required to position the spindle correctly while carefully turning the thimble to move the spindle down to the bottom of the hole before the reading can then be taken.
7. Tube Micrometer
A tube micrometer is a measuring device that has a rounded anvil and a flat spindle. This type of micrometer is designed specifically to measure the wall thickness of tubing and pipes.
Tube micrometers are available with four different types of anvils, which include pin, spherical, and cylindrical.
The idea is that the anvil has a small rounded surface, which has a smaller radius than the object being measured. This ensures it provides point contact against concave surfaces such as tubes and pipes for precise readings.
8. Non-rotating Spindle Micrometer
A non-rotating spindle micrometer is a precision measuring device where the spindle does not rotate as it comes into contact with the item being measured. This ensures the spindle does not apply a rotational, twisting force to the object that may damage delicate items.
On a standard micrometer the thimble rotates the spindle as it moves closer or farther away from the anvil. The rotating spindle mechanism twists like a screwdriver which can cause problems with certain applications, hence the need for the non-rotating spindle.
A blade micrometer, described above, is an example of a non-rotating spindle micrometer. The design demands a non-rotational spindle because if the blade spindle twists it essentially drills into the object being measured. Furthermore, the spindle may not align correctly with the anvil.
9. Sheet Material Micrometer
A sheet material micrometer is a handheld precision measuring instrument that is designed specifically for measuring sheets of material.
The deep frame design of a sheet material micrometer allows you to place sheet materials in between the frame to measure their thickness. These micrometers will typically use ball anvils, the rounded edge will provide you with the ideal contact needed for more accurate readings.
10. Disc Micrometer
The disc micrometer is a precision measuring device with two disc-shaped measuring faces on the anvil and the spindle. This feature makes the disc micrometer suitable for taking measurements of many awkward shaped objects, such as ridges and gear teeth. They are also commonly used for fragile material that is easily deformed, such as foam, rubber sheets, paper sheets, and film.
A disc micrometer is particularly ideal for taking the readings of gear components as you can accurately determine the tangent line. This is because the disc anvil offers a wider spread, this will comfortably rest flat across the gears without losing the anvil into the gear teeth.
They also work well with deformed and fragile material as the disc spreads out the force at the point of contact. This would otherwise compresses the measuring object which could skew the readings slightly.
11. Snap Micrometer
The design of a snap micrometer allows for speed and ease of use. A typical application would be the repeated process of checking the required measurement of identical items.
The spindle ‘snaps’ into place instead of being rotated by hand. the snap feature uses a spring-loaded spindle, applying the same amount of force when taking measurements. This consistency in applied force improves the accuracy of taking repeated measurements (repeatability). It also reduces the error margin when operated by different users (reproducibility).
Types of Micrometers Conclusion
The main consideration when choosing a micrometer for your application is the suitability of the micrometer type for its intended use. Once you’ve decided on the type of micrometer you need, its important to consider other specifications such as resolution and accuracy.
Once you know what type of micrometer you need and what specifications are suitable for your use, you will want to consider an analogue or digital model. Although generally more expensive, digital micrometers offer many advantages over analogue models, ease of use, higher resolution, and data output to name a few.
You can browse our range of digital micrometers here.