The dial on these gauges displays size deviations in real time. These gauges measure small slots and bores in precision parts, such as electronics, where even small size deviations can cause inefficiencies. Thanks to its full-ball design, the end of these gauges makes 360° contact inside the bore, so it's easier to center in tight spaces than anvil or spring-loaded contacts. This symmetrical ball is also less likely to tilt within the bore than half-ball gauges, which helps to avoid skewed measurements from improper placement.

Insert the probe into a bore and turn the knob on the handle to expand the contacts. To check size deviations, 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. To find the bore diameter, use a micrometer to measure the distance across the contacts.

Check a hole’s diameter and detect out-of-roundness problems. Often used to test engine cylinders and machine components, these gauges catch issues with roundness and taper. They have the most common design for bore gauges, which is a two-point contact system. The dial head’s highly sensitive jeweled bearings resist wear for a long service life.

To use these bore gauges, set a baseline measurement with a ring gauge, calibrator, micrometer, or caliper. The variation from the set measurement displays on the dial right away, so there’s no need for conversions. Swap out the anvil to measure bores of different diameters. Marked by size, the anvils are quick to spot and select.