Outside micrometers are precision measuring instruments that use a calibrated screw to measure the length, width, or outside diameter of an object. An outside micrometer consists of a stationary anvil and a moveable spindle that measure a workpiece by the space it occupies between the two measuring faces. Rotations of the micrometer’s screw amplify small distances that cannot otherwise be measured directly, translating those turns to a measurement that can then be read from a scale, dial, or electronic display. Common accessories for micrometers include cases, input/output cables, and stands.

Outside micrometers are commonly made of steel, and their measuring faces may have carbide tips for additional hardness and to help extend tool life. They may also have a finish to help resist corrosion, such as stainless steel, for reduced reflective glare.

When selecting the appropriate outside micrometer for an application, consider the material type, system of measurement, and maximum measurement.