What is the primary purpose of a micrometer?

• A. To measure large dimensions with rough accuracy
• B. To measure small dimensions with high precision
• C. To measure temperature
• D. To cut metal

Answer: (B)

Micrometers are built to measure small dimensions with high precision. A finely threaded screw shifts the spindle toward the anvil in tiny, controlled steps, and the combined reading from the main scale and the thimble lets you determine a dimension to a very fine tolerance—often to the nearest 0.01 mm or 0.001 inch, depending on the unit. This precision makes them ideal for checking parts like bearing diameters, valve stems, or shim thicknesses where even small differences matter. It isn’t the right tool for measuring large dimensions—that’s what tape measures or calipers are for—and it isn’t used to measure temperature or to cut metal. Its primary role is accurate measurement of small features.