Measure the inside diameter of holes and cylindrical bores, as well as identify out-of-roundness problems. These gauges are often used to test engine cylinders, machine components, and other parts for issues with roundness and taper. They have the most common design for bore gauges—a two-point contact system. Even if the gauge is tilted, an internal pendulum balances the contact points at the true center of a hole. Hollow grips make these gauges easy to hold and prevent heat from your hands from skewing accuracy. For a long service life, the dial head has highly sensitive jeweled bearings that resist wear. Its plastic cover protects against scratches and drops.

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.