Check roundness, taper, and diameter near the bottom of bores—the flat bottom on these gauges positions the anvil against the base of the hole. Because they reach down into bores, they are a better choice for measuring deep holes than calipers or inside hole micrometers. They are comparison gauges—the dial will display the magnitude of variation from the set measurement. Set your desired measurement with a ring gauge, bore gauge calibrator, micrometer, or caliper.

The anvil on the gauges extends out and contacts two points to take measurements. Swap the included anvils to measure bores with different diameters. An internal pendulum keeps these gauges centered as they slide into a bore and positions the anvils perpendicular to the bore surface. This results in more contact with the bore for consistent and accurate measurements. These gauges have hollow grips for easy handling. They also prevent body heat from causing the material of the gauge to expand and impact accuracy. A plastic cover on the dial protects it from drops and scratches.