Which of the following items can affect a micrometer's measurement?

• A. Dust
• B. Oil
• C. Burrs
• D. All of the above

Answer: (D)

A micrometer measures size by the precise contact between its spindle and anvil, so any material or surface imperfection that gets between those faces or on the part being measured can shift the reading. Dust between the jaws can act like a tiny spacer or cause uneven contact, leading to a reading that isn’t the true size. Oil on the faces or on the part creates a slippery film, which can cause drift or inconsistent seating and thus an off reading. Burrs, raised edges on the part, change the actual contact plane the micrometer uses, so you might be measuring the burr height rather than the intended surface, producing a higher or otherwise incorrect value. Because each of these factors can distort the measurement, all of the above can affect a micrometer’s measurement. To ensure accuracy, keep surfaces clean, inspect for burrs, and remove oil before measuring.