Which tool would you use to measure the outside diameter of a shaft?

• A. Vernier caliper
• B. Dial indicator
• C. Depth gauge
• D. Micrometer caliper

Answer: (D)

Measuring the outside diameter of a shaft needs a tool that provides a precise, uniform contact with the part’s external surface and a fine, controllable advance. The micrometer caliper does this with a spindle and calibrated screw that move in very small steps, usually readable to thousandths of an inch or hundredths of a millimeter. This level of precision is essential for shafts that must fit tightly into bearings, housings, or other components, where even a small error can affect clearance and performance. A vernier caliper can measure external diameters as well, but its overall precision is lower and more susceptible to user alignment errors. A dial indicator is used to show small deflections or runout, not the exact fixed diameter, and a depth gauge measures depth not diameter. So for accurate external measurements on shafts, the micrometer caliper is the appropriate tool.