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Go/No-Go Gaging Basics
Guide · Updated October 27, 2026
Go/no-go gauges answer one question fast: is the feature inside its limits? No reading, no math, which makes them ideal for production. Here's how to choose the sizes, how accurate the gauges need to be and how to keep them honest.
Keep your gauges honest
Set a comparator or check a micrometer with a stack from the free Gage Block Calculator. Free, no login.
Which end is which
| Feature | Go | No-go |
|---|---|---|
| Hole (plug gauge) | Minimum hole size | Maximum hole size |
| Shaft (ring or snap gauge) | Maximum shaft size | Minimum shaft size |
Worked example
A hole is 0.5000–0.5010 in. Go pin: 0.5000 in, plus tolerance. No-go pin: 0.5010 in, minus tolerance. With 10% of the 0.0010 in part tolerance, each gauge is held within about 0.0001 in. Gauge tolerances go into the part limits, so the gauge may reject a borderline good part, but a bad part can't pass.
Step by step
- Read the limits: Get the minimum and maximum size from the drawing.
- Pick the gauges: Go = maximum material limit, no-go = least material limit. Choose a gauge class about 10% of the part tolerance.
- Verify the gauges: Check the gauges against a micrometer or comparator set with gage blocks.
- Gauge the part: The go gauge should enter or pass under its own weight, with no force. The no-go must not.
- Record and react: Log results, and act on trends before parts drift out.
Tips
- Never force a go gauge. Force wears it and can hide an undersize hole.
- Let parts cool before gauging. Hot parts read large.
- For sizes go/no-go can't show, see bore gages and micrometers.
- Set calibration intervals for gauges just as you would for blocks: calibration interval.
FAQ
What does go/no-go mean?
A go gauge must fit the part and a no-go gauge must not. If both happen, the feature is within its limits.
Which size is the go end of a plug gauge?
The go end is the minimum hole size (the maximum material limit) and the no-go end is the maximum hole size. For a ring gauge on a shaft it's the other way round: go = maximum shaft, no-go = minimum shaft.
How accurate does a go/no-go gauge need to be?
A common rule of thumb is a gauge tolerance of about 10% of the part tolerance. Gage pins come in classes such as ZZ, Z, Y, X and XX, from widest to tightest tolerance.
Can a part pass go/no-go and still be bad?
Yes. A go/no-go gauge checks size limits, not roundness, taper or position. An oval hole can pass. Measure critical features as well.
How do I check my plug gauges?
Mic them with a micrometer checked against gage blocks, or compare them on a bench comparator zeroed on a gage block stack. Build stacks free at gageblockcalc.com.
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General shop information only — follow your gage manufacturer's instructions and your quality system.