Which item is used to calibrate measurement instruments with highly accurate, known dimensions?

• A. Dial indicator.
• B. Drill press stop.
• C. Face mill.
• D. Gage block.

Answer: (D)

The main idea is using a reference with precisely known dimensions to set or verify the accuracy of measurement tools. Gage blocks are machined to extremely tight tolerances and finished to have very flat, parallel faces. Their exact thickness or length is certified and traceable to national standards, and they can be stacked or “wrung” together to create a wide range of precise lengths. This makes them an ideal normal for calibrating instruments like micrometers, calipers, height gauges, and dial indicators because you can rely on the blocks’ known measurements to check or adjust the measuring devices. The other items are a dial indicator (a device that measures small displacements), a drill press stop (a depth-control accessory), and a face mill (a cutting tool); none of these serve as a highly accurate, known-dimension reference for calibration.