Contents

• What is a caliper?
• What is an micrometer?
• What are the key differences between calipers and micrometers?

A caliper is a measuring instrument that measures the size of an object (be it the length, width or depth). They can feature outside jaws for external measurements or inside jaws for internal measurements, as well as a blade at the tip of a caliper for depth/thickness measurements.

Calipers can be supplied in several styles including:

• Analogue or vernier calipers, which require manual reading of a vernier scale.

• Digital calipers, which utilise an LCD display to provide an easy-to-read, higher accuracy measurement upto 4 decimal places. These tend to be the most popular.

• Dial calipers, which features a circular dial in the centre of the caliper, are much more commonplace than vernier calipers because of easier measurement reading.

Micrometers offer extremely high accuracy measurements of external and internal dimensions. They can be used to measure dimensions like the thickness, diameter, length or depth of a workpiece.

• External measurements are taken using outside micrometers.

• Internal measurements are taken using inside micrometers, also known as bore micrometers.

Outside micrometers utilise a thimble and ratchet to tighten two points, of which the workpiece will sit between and be held by. The distance between these two points (which can either be pointed or flat) will then be measured by the micrometer using either an analogue scale, dial or digital readout. The digital micrometers are proving to be more popular as measurements are easier to read (as well as eliminating user error from misreading a manual scale).

Inside micrometers measure specific inner areas or internal diameters of a component. Like outside micrometers, some models of inside micrometers feature a thimble and ratchet to tighten two jaws, of which the workpiece would be held internally. Three point bore micrometers, meanwhile, hold workpieces at three points, making them quicker and more efficient when measuring round internal diameters.

The primary difference and consideration to be made between calipers and micrometers is accuracy. In general (depending on the scale, model and range), micrometers will almost always provide a more accurate method of measuring components. A typical caliper, for instance, will have a resolution of 0.01mm or 0.0005”, whereas a micrometer of similar specification would have a resolution of 0.001mm or 0.00005”.

Accuracy can also be attributed to the mechanism used to set the tool in order to perform the measurement operation. With calipers, you either push the jaws together (outside measurements) or pull the jaws apart (inside measurements) until the user believes the component is secure between them. However, there is more room for misjudgement in whether the jaws are perfectly secured, causing the higher runout in accuracy. Micrometers, through the thimble system, means that the user will tighten this until it can go no tighter, hence reducing the chance of user-created measuring errors.

However, there is a trade-off with this increased accuracy, in that the range of measurements that can be performed on micrometers is often less than those on calipers. Typical ranges of micrometers can measure from between 0-25mm (0-1”) up to 75-100mm (3-4”), whereas calipers commonly measure from 0-300mm (0-12”). So not only do calipers cover a higher maximum range of values, but can also start measuring from zero; micrometers often have to begin measuring from a certain minimum length (which is dependant on the max value).

Another common distinction which may influence purchasing decisions is the range of applications each measuring unit can perform. In this regard, calipers can be considered more cost-effective. Modern calipers often feature 4 jaws on each unit, with 2 used for inside measurement and 2 for outside measurement. Not only does this save money by not having to purchase two instruments for different applications, but it also increases user productivity by not having to switch tools between inspection operations.

Conversely, micrometers can only usually be used for either outside or inside measurements. Therefore, 2 models will need to be purchased to perform both types of measurement. Furthermore, users will need to factor in switching tools when using micrometers, especially when performing bulk measurement or inspection tasks. Not only this, but the actual operation of using a thimble to ‘screw’ the micrometer into place is far more time-consuming than adjusting the scale on a caliper.

In conclusion, whether you should choose a caliper or micrometer will depend on your application, required accuracy levels and budget. Whilst calipers offer a slightly more cost-effective solution with a wider range of measurements and both internal and external measurement possible with the same unit, micrometers provide precise and reliable measurements. For batch work, we would recommend calipers, whereas for smaller measurement or inspection tasks, micrometers would be the way to go.

Cutwel supply and stock one of the UK's biggest range of measuring and inspection tools from market leading brands including Mitutoyo, Bowers, Sylvac, Moore & Wright, Baty, Insize and Johs Boss (JBO). We supply a comprehensive range of calipers with digital, vernier or dial output, for a variety of applications including crimp height, measuring hole centres, tube thickness, arc radius and gear tooth measurements. Similarly, we offer both inside and outside micrometers with digital, dial or vernier readouts. Applications for our micrometers include large range, grooves, splines, keyways, screw thread, limits, sheet metal, crimp height, wire, can seam and bore measurements.