Bring the micrometer near the desired opening for the part to be measured by rolling the micrometer along the arm or hand.
Close the micrometer on the part until the anvil nearly touches. Ease the micrometer the rest of the way to contact with the part using the ratchet stop until the ratchet clicks one time.
Count the number of lines showing on the barrel scale. Each line represents .0250 of an inch.
Find the line on the thimble that lines up with scale on the barrel. The number will indicate .001 of an inch.
Add the numbers from Step 3 and Step 4 together. The sum of the two numbers will be the measurement in thousandths of an inch.