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Vernier micrometer graduation value

Aviation Mechanic General (AMG) practice question 23 of 33 on Aircraft Materials, Hardware, and Processes. ACS element AM.I.E.K6 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONOn a micrometer equipped with a vernier scale, each vernier graduation represents

  1. A0.001 inch.
  2. B0.0001 inch.
  3. C0.025 inch, the same as one barrel division.
Show the answer and explanation

Correct answer: B. 0.0001 inch.

  • A — incorrect One thousandth of an inch is the value of each thimble graduation, not the vernier graduation.
  • B — correct The vernier graduations divide the 0.001-inch thimble division into 10 equal parts, each equal to 0.0001 inch.
  • C — incorrect Each barrel graduation equals 0.025 inch, set by the 40-thread-per-inch lead screw. The vernier scale reads far finer than that.

BACKGROUND

A micrometer has three scales. The barrel scale graduations are 0.025 inch apart, established by the lead screw of 40 threads per inch. The bevel edge of the thimble is divided into 25 parts, so each thimble graduation equals 0.001 inch. Some micrometers add a vernier scale that divides the 0.001-inch thimble division into 10 equal parts, each equal to 0.0001 inch, making it possible to read directly to ten-thousandths of an inch. The vernier line to be read is always the one aligned exactly with any thimble graduation. The barrel reading, thimble reading, and vernier reading are added to obtain the final measurement.

STUDY TIP

Keep the three scale values straight: barrel 0.025 inch, thimble 0.001 inch, vernier 0.0001 inch.

KEY POINTS

  • Barrel graduations are 0.025 inch, from a 40-thread-per-inch lead screw.
  • Thimble graduations are 0.001 inch.
  • Vernier graduations are 0.0001 inch.

SOURCES

  • FAA-H-8083-30B ch11 "Vernier Scale"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.