Go No Go Gage
What does a Go/No-Go gage tell a machinist that a caliper does not?
It tells whether the feature is functionally acceptable within limits, not the exact measured size; it is a quicker acceptance test than an actual dimension reading.
Why is a Go/No-Go gage used so often in CNC production?
Because it is fast, repeatable, inexpensive, and ideal for in-process control when the goal is to confirm acceptance rather than record a numeric dimension for every part.
Can a part pass Go/No-Go and still fail elsewhere?
Yes; a fixed-limit gage checks only the feature and condition it was designed for, so other characteristics such as runout, surface finish, perpendicularity, or hole location may still require separate inspection.
A Go/No-Go gage is a fixed-limit inspection tool that gives a pass/fail result for a feature’s size or form against its tolerance band. The Go side must fit or pass; the No-Go side must not fit or pass. It verifies functional acceptance at material condition boundaries, ensuring interchangeability without measuring exact dimensions.
In CNC machining, Go/No-Go gages are used at in-process or final inspection to verify holes, pins, threads, slots, and form features without setting up a CMM or micrometer for every part. An operator checks a bored hole with a plug gage or a turned shaft with a ring gage immediately after machining. If the Go side enters correctly and the No-Go side does not, the part is accepted and moves on. This matters most in high-volume work because it cuts inspection time, catches tool wear quickly, and gives an immediate functional check that the part will assemble. The gage itself carries a small portion of the product tolerance—often around ten percent—so the inspection system does not overshadow the actual feature. The same principle applies to form and profile gages in millwork and edgebanding, where groove widths and edge profiles must fit consistently even without a numerical readout.
Forcing the No-Go side: Pushing a No-Go gage into the feature falsely accepts or rejects the part. It must never be forced; heat, burrs, or chips can let a borderline bad part ship to assembly.
Checking a dirty or burred feature: Chips, coolant, burrs, or plating buildup can stop the Go side from entering even when the dimension is good. This creates false rejects that halt production and lead to unnecessary tool offsets.
Using the wrong gage or tolerance class: A plug gage checks holes, a ring gage checks shafts, and thread gages are geometry-specific. Mixed prints or metric-inch confusion can make a conforming part appear nonconforming.