0.005mm.
A spiral micrometer, also called a micrometer, is a precision measuring tool. Micrometer is also called a spiral micrometer. The first such measuring tool was patented by French inventor Jean Laurent Palmer in 1848 and was called a "threaded caliper with circular vernier frame." Today, we still use this characteristic feature to manufacture outside micrometers. The introduction of the micrometer into the mechanical world began with the visit of two American engineers, Joseph R. Brown and Lucian Sharpe, to the Paris Exhibition in 1867. Their attention was attracted by Palmer's invention and they were very interested. Improvements to Palmer's design were made in large quantities and successfully marketed by the two partners. When the Swiss company TESA decided to manufacture an outside micrometer, they repeated a story that had happened in the past, making this product the company's first. Except for a few cases (such as micrometers for measuring gears), the micrometers we use follow Abbe's principle, just like comparators. The micrometer spindle is processed by a modern grinding machine. The thread profile is very precise and the pitch deviation is negligible. The processing conditions ensure the extremely low measurement uncertainty of the micrometer.