With a calibration certificate traceable to NIST that says they've passed a test for accuracy, you can trust these gauges to confirm if your object's outer diameter is within tolerance. They're also known as snap gauges because they snap onto rods, shafts, and other cylindrical objects. To maintain their accuracy over time, they have a hardened steel frame and spindle that withstands flexing and temperature changes.

Indicators—Attach variance indicators to measure the difference between your part’s actual diameter and the expected diameter. They also come with a calibration certificate traceable to NIST that states they’ve passed a test for accuracy.