Micrometers use a rotating spindle to measure the thickness of small items. The spindle presses the object to be measured against an anvil. The rotation of the spindle is converted to a distance measurement, which is listed on the micrometer's sleeve. Over time, the surfaces of the spindle and anvil may wear down, which increases the distance between the two parts. If you do not adjust the micrometer to account for this change, its measurements may no longer be accurate.
Place a clean piece of paper between the micrometer's spindle and anvil. Tighten the thimble on the end of the spindle until the micrometer lightly grips the paper. Pull the paper out slowly to clean the inner surfaces of the anvil and spindle.
Tighten the thimble slightly to completely close the micrometer. Make sure the face of the spindle is in solid contact with the anvil.
Compare the index line on the spindle with the zero line on the sleeve. If the two lines do not match up, adjust the micrometer by turning the sleeve with a spanner wrench. Keep the spindle and sleeve together while making your adjustments.
Tighten the spindle nut if it has loosened over time. To access the spindle nut, turn the thimble counterclockwise. Use the spanner wrench to tighten the nut. Do not overtighten the nut as this can impede the spindle's movement. Turn the thimble clockwise to hide the spindle nut when you are finished with your adjustments.
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