Measuring, as in taking linear measurements, such as length, width, thickness, depth, or diameter, is probably as old as humanity itself. Since the dawn of time, humans have used different measures to quantify the distance between two points; finger-length, elbows, steps, meters, feet, yards.
With advances in technology, our measurements became so precise that a regular ruler can't measure them correctly. That's why machinists and other precision manufacturing specialists used special tools to take precise measurements, most notably calipers and micrometers.
Micrometers and calipers are probably some of the most important measuring tools in machining and engineering, as they can measure thickness, diameter, length, and width. One thing they have in common is that they're both precision measuring tools, but their main differences lie in their accuracy and the types of measurements they can take.
Micrometers, also called micrometer calipers or screw gauges, are extremely precise measuring tools for external measurements, most notably thickness, though they can be used for measuring small external diameters.
The term "micrometer" generally refers to outside micrometers as those are the most widely used types of micrometers. They're not as versatile as calipers and are usually limited to only one type of measurement, which is why there are several different types of micrometers, including outside micrometers, depth micrometers, and inside micrometers.
They come in a variety of measuring ranges which differ every 25mm, or approx. 1 inch (depending on the model). The measurable ranges include 0-25mm or 0-1", 25-50mm or 1-2". There are models that go beyond that, some of them using 0-600mm or 0-24" ranges, depending on the size of the frame.
This means that your micrometer has to match the target that's being measured. More specifically, the measured target has to be within the micrometer's measuring range. To make the best use of a micrometer, make sure to purchase one with replaceable anvils and spindles, or you may have to buy more than one model.
Lastly, there are two categories of micrometers on the market: analog and digital. Analog micrometers are most widely used across different industries, as they don't rely on batteries. Despite that, digital micrometers equipped with an LCD display are becoming increasingly popular due to their ease of use.
Calipers are precise measurement tools that can accurately measure up to 0.01mm, or 0.001 inches. They feature a main scale attached to an upper jaw, which has a metric scale on one side, and an imperial scale on the other, measuring in millimeters and inches, respectively.
However, the lower jaw has a smaller sliding scale, called the Vernier scale. Named after a mathematician Pierre Vernier, this is a visual tool that allows you to obtain an accurate measurement between two graduation lines on a linear scale, eliminating human estimation error. Some types, like dial calipers, have dial indicators instead of a Vernier scale. Likewise, digital calipers feature an LCD display and are becoming increasingly popular due to their ease of use.
Calipers, though 10 times less accurate than micrometers, are widely used for their versatility, as they can take several different measurements. For example, larger jaws can be used for taking external measurements, such as an outside diameter, with smaller jaws intended for internal measurements, like inner diameters.
In addition to measuring inside and outside measurements, all calipers are equipped with depth measuring blades, allowing machinists to accurately measure the depths of specific components.
Most calipers found in standard toolboxes measure up to 152.4mm or 6 inches. However, as with micrometers, these also come in different sizes.
There are four key differences between micrometers and calipers:
Vernier calipers are less accurate measuring devices, but they have broader use, as they can take inside, outside, and depth measurements accurately up to one-thousandth of an inch (0.001") or a hundredth of a millimeter (0.01mm) if it uses a metric scale.
Micrometers are measuring instruments for extremely precise measurements. They're accurate up to 0.001mm (one-thousandth of a millimeter) or 0.0001 inches (or ten-thousandth of an inch).
While there are some variations in accuracy, due to the accuracy rating, you'll find that micrometers have ten times higher accuracy than caliper measurements. Analog calipers typically have a ±0.02mm or ±0.001in tolerance, meaning that a 0.50mm measurement is considered within 0.49mm to 0.51mm, or 0.018in to 0.020in range.
Calipers are simpler in design and thus more user-friendly and easier to use. On the other hand, micrometers require more finesse, and if you're not careful, measuring the same component five times can result in five different measurements.
Even the temperature of micrometers can have a tiny impact on measured values in high precision work. To prevent heat transmission from the user's hands, certain micrometers contain insulated pads.
As previously mentioned, calipers are more versatile than micrometers, which are limited to singular measurements. Additionally, calipers' jaws can be used for marking tasks — though this is something we strongly advise against.
Calipers often have a wider measurement range, typically from 0-6 inches, while micrometers have smaller measurement ranges, typically 0-1 inch or 1-2 inches.
Micrometers offer less range and are considered more of a specialized tool compared to calipers. They're mostly used in high-precision machine fabrications and parts manufacturing, so you'll definitely know if you need one.
Calipers are a good place to start precision machining and learning how to read precise measurements. They're also quite versatile, which makes them suitable for work in various industries, from machining to electrical work, mechanics, metalworking, and machining. You generally want to use calipers when measuring inner diameters of tubing, major dials of threads, or other types of length/diameter/depth measurements.
Both calipers and micrometers are precision measuring tools, but they're ultimately very different. Where micrometers are more specialized and offer a narrower range of measurement, calipers offer a wider range of applications, compromising accuracy to achieve versatility.
Both have unique advantages and drawbacks, but they're still two of the most significant precision measurement tools in a machinist's toolbox. If you want to learn more about precise measuring and inspecting, make sure to visit Reid Supply and check out their extensive collection of professional literature.