A micrometer is used to measure small items, usually in an engineering or manufacturing environment. Most micrometers use a set of calipers to measure the outside of an item, but there are also specialized micrometers that can measure the inside of a hole or depth of a slot. Universal micrometers come with interchangeable parts that allow the user to measure different types of items with just one tool.
The First Micrometer
James Watt invented the first micrometer in 1772 as a way to improve the production of large equipment during the Industrial Revolution. Manufacturing companies were having trouble assembling consistent products because there was no suitable way to precisely measure small distances. Watt's micrometer consisted of two jaws that could be moved up and down by turning a threaded spindle. The piece to be measured is placed between the jaws, and the micrometer is adjusted until the jaws touch the item. The dial displays the distance between the jaws.
The Lord Chancellor
In 1805, Henry Maudslay developed his "Lord Chancellor" micrometer. The design was similar to Watt's, with two plates connected by a threaded screw. The screw contained 100 threads per inch and included an index wheel with 100 marks around the outside. This gave Maudslay's micrometer amazing accuracy for the time, allowing it to measure down to one ten-thousandth of an inch.
A former employee of Maudslay, Joseph Whitworth improved upon the Lord Chancellor's design, introducing a micrometer that could measure to within one millionth of an inch. The design was so innovative at the time that it was displayed at the Great Exhibition of the Works of Industry of All Nations in London in 1851.
The first portable micrometer was built in France by Jean Palmer. It was small enough to be operated with one hand, making it possible to measure metal sheets or other parts at any point on the assembly line. While the design has been refined over the years, Palmer's portable micrometer was very similar to the models in use today. Known as the Systeme Palmer, this micrometer design was shown at the 1867 Paris Exposition.
Brown and Sharpe
American engineers J.R. Brown and Lucian Sharpe saw the Systeme Palmer in Paris and realized it was the solution to a problem that had been plaguing them. At the time, there was no good way to measure sheet metal, leading to customers returning shipments because they were not the correct thickness. They modified Palmer's design and received a patent in the United States in 1899, leading to the first mass-produced micrometer.