Which set of scales is used on an analog micrometer to form the final reading?

• A. Sleeve scale only
• B. Vernier scale only
• C. Thimble scale only
• D. Sleeve scale, Vernier scale, and Thimble scale

Answer: (D)

An analog micrometer forms its final reading by combining information from three scales: the sleeve scale (main), the vernier scale, and the thimble scale. The sleeve gives the main size in whole units (millimeters or inches). The thimble provides the fraction of that unit, showing how far beyond the last sleeve mark you’ve measured. If a vernier scale is present, it lets you interpolate between marks for even finer precision by indicating a tiny additional fractional amount when a line on the vernier aligns with a line on the fixed part. By reading the sleeve for the baseline, then the thimble for the fractional part, and using the vernier for the final refinement, you obtain the exact measurement. For example, you might read 12 mm on the sleeve, see 0.42 mm on the thimble, and the vernier alignment indicating an extra 0.02 mm, giving a final reading of 12.44 mm. That combination can only come from using all three scales, which is why the set including sleeve, vernier, and thimble is the correct concept.