One complete revolution of the thimble on an English micrometer corresponds to how many inches?

• A. 0.025 inches
• B. 0.001 inches
• C. 0.125 inches
• D. 0.050 inches

Answer: (A)

One complete turn of the micrometer’s thimble moves the spindle by the pitch of the screw. For an English micrometer, the screw has 40 threads per inch, so one revolution advances the spindle by 1/40 inch, which is 0.025 inch. The thimble divisions let you read fractions of that travel, but the full turn itself corresponds to 0.025 inches. The other options would correspond to different multiples of turns (for example, two turns would be 0.050 inch, five turns 0.125 inch), not a single full revolution.