GO and NO GO Gauge Limits

Ideal gauge sizes

For a hole, the ideal GO plug corresponds to the lower workpiece limit and the ideal NO GO plug to the upper limit. For a shaft, the GO ring or snap gauge corresponds to the upper limit and the NO GO gauge to the lower limit. A hole bounded by 20 and 20.03 mm therefore has ideal gauge sizes of 20 and 20.03 mm.

Manufacturing deviations

Those two numbers are insufficient for manufacturing a real gauge. The applicable gauge standard and approved inspection plan define the gauge tolerance, its placement and the wear limit. The gauge plan tab does not select those values. It adds your signed lower and upper deviations to the ideal sizes.

Wear and acceptance

The wear limit deviation is referenced to the ideal GO size. It is not the amount worn away from a new gauge. Initial zero deviations are examples only. Gauge length, form, calibration and measurement uncertainty must be addressed before any manufacturing or acceptance decision.

Follow the limit direction for shafts

Choose a shaft lower limit of 24.98 mm and upper limit of 25 mm. Workpiece tolerance is 25 − 24.98 = 0.02 mm, or 20 µm. Ideal GO size is 25 mm and ideal NO GO size is 24.98 mm. These values are not the gauge manufacturing interval. They only show which workpiece limit the ideal size model uses.

With a real gauge plan, check that every deviation is referenced to the relevant ideal gauge size. A deviation from nominal workpiece diameter may have a different reference from a deviation from nominal gauge size. Review units carefully. Entering a small deviation specified in micrometres as millimetres greatly changes the result. This preliminary calculation cannot establish acceptance or rejection without form and measurement uncertainty assessment.

Frequently asked questions

How do you calculate GO and NO GO gauge sizes?

In this example, the ideal hole gauge rule gives GO size 30 mm and NO GO size 30.04 mm for workpiece limits 30 mm and 30.04 mm. This preliminary calculation excludes gauge manufacturing tolerance, wear allowance, calibration and measurement uncertainty, which must be specified before manufacturing or acceptance decisions.

Calculate with these values