An anvil is one of the parts that make up a micrometer. Located at the head of the micrometer, the anvil is a measuring face, opposite the spindle. It is between the anvil and the spindle faces that an object is placed in order to measure its size. In order to properly position the anvil on a micrometer, place the object needing to be measured immediately between the anvil and spindle. Using the thimble and ratchet, adjust the faces so that the object is snuggly held between them. Switch on the spindle lock in order to keep the anvil and spindle faces at the necessary location. Then, remove the object and read the micrometer. It is important to keep the anvil clean before and after completing a measurement. Any amount of dust or built up on the anvil could impact the accuracy of the micrometer.