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A micrometer screw is a handheld device used to measure very tiny lengths and thicknesses. Examples of its measurements include the width of tubes or the thickness of a wire. Micrometer screws come in at least three different design variations, but they all use a finely calibrated screw to make accurate measurements. A micrometer screw can be calibrated to take several different kinds of units of measurement, which makes them useful in several different disciplines.
Most micrometer screws have four important parts: a handle, the calibrated screw, the frame, and an anvil. The frame holds the anvil at a distance from the screw. As the screw is twisted, it lessens or increases the distance between the end of the screw and the anvil, much like a vice. Some micrometer screws simply have a handle and the screw attached. It is held up against the object to be measured much like a ruler.
All micrometer screws are carefully manufactured so that the distance between the screw threads is the same down the entire length of the screw. That way, when the screw is twisted, it can give an accurate measurement. The base of the screw will be marked with lines showing each unit of measurement. When matched up with those on the handle of the micrometer screw, the user can see the measurements made.
A micrometer screw can have various attachments that can be screwed on and off in order to measure different objects. They also come in various designs to facilitate measuring different kinds of objects and distances. Individuals can purchase a micrometer screw to specifically measure widths, slits and holes. The screw can also measure depths, diameters, and the thicknesses of tubes. They are available in both metric and US systems of measurement.
A French astronomer named William Gascoigne is credited with creating the first working micrometer in the 1600s, though the concept existed before then. He used it to measure the distances between stars as could be seen through his telescope.
Before this, a sextant was used to measure the distance between the sun and the horizon for ship navigation. This was only a naked eye measurement, and Gascoigne realized that a much more accurate measurement could be taken through the use of a screw. With these measurements, he was then able to perform calculations related to the size of the planets and stars he was seeing in the sky. In time, the accuracy of the micrometer led to its development for measuring terrestrial objects. They began to be widely manufactured in the 1800s.