A micrometer is a device designed to make a very accurate measurement where accuracy is usually not possible. Inside and outside micrometers, as well as channel depths, are a few types of the devices. A screw-gauge micrometer uses a shaft, or spindle, that is advanced or retracted using precisely machined screw threads inside the handle. The gauges on the handle are then read to determine the measurement. Screw-gauge micrometers can be produced in either English or metric units.
Choose the correct micrometer for your application, and set the screw on the object you are measuring. Make sure it is snug but not overtightened.
Use the micrometer's locking device to hold the spindle in place.
Remove the micrometer and read the linear gauge. This gauge will most likely be abbreviated so that "24" equals "0.24 inches" or something similar, depending on the micrometer you are using.
Using the horizontal line on the linear scale as a pointer, read the scale on the barrel. The number of increments on the barrel will depend on the size of the step between increments on the linear scale. For example, if the linear gauge is divided into quarter steps, the barrel will have 25 increments.
Combine the readings. In this picture, the linear gauge reads 5.5mm. Note that this particular gauge is not abbreviated. The linear gauge is divided into half steps, so the barrel gauge has 50 increments. This gauge reads "28," which is an abbreviation for "0.28mm." The combined reading, then, is "5.78mm."
Micrometers are very precisely machined and can be affected by extreme heat or cold and well as impact forces. Treat your micrometer carefully.