Check for sizing errors in small slots and holes. These bore gauges show deviation from a set diameter measurement on the dial. They’re often used in precision manufacturing to test electronics and small-scale prototypes. The full-ball probe makes 360° contact inside of bores, making it easier to center in tight spots than anvil or spring-loaded contacts. Since it’s symmetrical, the ball is also less likely to tilt and skew measurements than a half-ball probe. The dial head has a plastic cover to protect it from drops and scratches.

Insert the probe into a bore and turn the knob on the handle to expand the contacts. To check size deviations, first set the desired measurement with a ring gauge, bore gauge calibrator, micrometer, or caliper. The dial will display the magnitude of variation from the set measurement. Use a micrometer to measure the distance across the contacts and get the bore diameter. Swap out the anvil to check bores of different diameters.