PURPOSE: To provide selectability and changeability of the position and size of a measuring range by furnishing extension standard gauge(s) on the anvil and/or spindle of a micrometer.

CONSTITUTION: A component part to be measured is set between the surface 16 of an anvil 14 and the measuring surface 22 of a spindle 20. These surfaces 16, 22 are approached to the component part by rotating a thimble 18, and its reference position with respect to the body 24 of a micrometer gives a measuring value. The spindle 20 has a measuring range (a), and if the dimension to be measured lies within the range between a+b+c and b+c, it is possible to use the micrometer 10 with no help of any accessory component. If however the measuring range is between (c) and a+c, an extension standard gauge 30 is attached to the spindle 20 with the aid of a sleeve 40, which causes the measuring range to be between (c) and a+c. An appropriate one of the standard gauges 26, 28, 30 is applied to the sleeve 40 for constituting the measuring gap having different length.