What is the smallest division read by a vernier micrometer caliper?

• A. 0.001 inch
• B. 0.0001 inch
• C. 0.00001 inch
• D. 0.01 inch

Answer: (B)

A vernier micrometer is able to read finer than the main scale by using a vernier (thimble) scale that interpolates between the main scale divisions. The screw pitch in a typical imperial micrometer is 0.025 inch per full turn, and the thimble is divided into 50 equal parts. That makes each thimble division 0.025 / 50 = 0.0005 inch. The vernier mechanism subdivides one main-scale division into five equal parts, so you can resolve an additional 0.0005 / 5 = 0.0001 inch. When you line up the vernier mark with the sleeve marks, you read the main scale value plus the vernier value in 0.0001 inch increments, giving a smallest readable division of 0.0001 inch.