An outside micrometer consists of a C-shape frame with an anvil and a threaded spindle. The thread is precision ground to ensure uniform movement of the spindle toward or away from the anvil. The spindle moves as it is rotated in the stationary spindle nut. A graduated stationary sleeve and a graduated rotating thimble are the bases for determining measurement. A locking mechanism can be provided for holding an established reading. A friction thimble stop is also available to establish a uniform feel among individual users.
In addition to the standard outside micrometers, micrometers also exist with different anvil and spindle shapes for specialized applications. Blade micrometers are used for measuring narrow slots and grooves. The disc micrometers is used for measuring thin materials such as paper as well as for measuring the distance from a slot to an edge. Hub micrometers can be put through a hole or bore to permit the measurement of the hub thickness of a gear or sprocket. Screw thread micrometers measure the pitch diameter of screw threads.