What measurements would you take with a micrometer, and how do you read it?

• A. External dimensions; read sleeve scale and thimble; read to thousandths of an inch; ensure proper zero
• B. Internal dimensions; read dial indicator
• C. Length of tool only
• D. Temperature of metal

Answer: (A)

The outside micrometer is used to measure external dimensions with high precision. To read it, you combine two scales: the sleeve (barrel) scale and the thimble scale. The sleeve gives the main portion of the measurement in inches, while the thimble provides the small fractional part. When you read, first note the value on the sleeve, then read the line on the thimble that lines up with the sleeve’s index line to get the additional thousandths of an inch. Add the two readings together and you have the measurement to the nearest thousandth of an inch. Before taking a reading, ensure the zero is true by closing the jaws with a light, consistent touch (often using the ratchet) and verify that the zero on the thimble aligns with the sleeve’s zero. This practice prevents offset errors and confirms the micrometer is calibrated.