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What is a Depth Micrometer?

Patrick Roland
Patrick Roland

A depth micrometer is a sensitive tool that is used to measure the depth of small holes and bores. Used by engineers and mechanics, this device has a series of unique pieces that help it dial in an exact measurement. Reading depth micrometers is a precise science that must be performed carefully. For those without the time or patience, technology has provided micrometer enthusiasts with a digital option for even better readings.

Knowing the precise measurement of a bore opening is important business for engineers and mechanics. It can mean the difference between a perfectly functioning engine and a disaster. The key to properly using the depth micrometer is patience, because the readings are highly sensitive, and hurrying through a measurement will not provide accurate results.

Man with a drill
Man with a drill

A depth micrometer is comprised of five key parts that make this stubby, screwdriver-looking device. The spindle is the most important part of the depth micrometer calibration process because it is the thin probe at the end of the device that performs the actual measuring. Further up that rod, the base of the measuring device is the spacer and spindle lock screw that are used for tightening and loosening. The actual measurements are taken on the thickest part of the micrometer, the rounded handle-like parts called the sleeve and thimble. These parts are marked with numbers representing measurements that can be adjusted to get precise readings of a bore.

In order to get that precise reading, the micrometer's spindle must be gently inserted into an opening that needs to be read. Slowly turning the sleeve will descend the spindle further into the hole. Turning this dial until the spindle touches the end of the opening will result in an accurate measurement. This measurement can be read by removing the micrometer from the opening and looking at where the numbers are lined up along the sleeve and thimble.

With anything measured by hand, there always are risks of user error, and it is possible to not get a perfect reading with a traditional depth micrometer. Measurement has become more accurate with the invention of the digital depth micrometer. This machine resembles the previous hand-controlled models, except that it has a small digital screen near the end. By simply inserting the spindle into a bore, the exact depth measurement appears on the screen for a more accurate reading.

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      Man with a drill