Ring Gage

Ring gages are fixed-limit or reference gages used in dimensional inspection. Go/no-go ring gages come in pairs: the "go" gage should pass over the part (verifying maximum material condition), and the "no-go" gage should not pass over the part (verifying minimum material condition). Setting ring gages (master rings) are used to set the zero reference on comparative measurement instruments like air gages, bore gages, and snap gages.

Calibration of ring gages involves measuring the bore diameter using a precision bore measurement system, typically a calibrated CMM with a small-diameter probe, an internal micrometer, or an air gage comparison method. Measurements are taken at multiple positions and orientations to evaluate roundness, straightness, and taper. The calibration certificate reports the measured diameter, roundness error, and surface condition assessment.

For calibration management, ring gages are subject to wear that gradually increases their diameter (for go gages) or changes their geometry. Wear rate depends on the material (chrome steel, carbide, ceramic), frequency of use, and the parts being gaged. Chrome steel ring gages in heavy production use may need calibration every 3-6 months, while lightly used master rings may have 12-month or longer intervals. Ring gages should be inspected for visible wear, scratches, and corrosion between calibrations. Worn ring gages produce false accept decisions, allowing oversized parts to pass inspection.