The Logic of Limit Gauging
A go/no-go gauge — called a limit gauge (限界ゲージ) in Japanese — embeds the tolerance limits directly into a physical tool. Instead of measuring the dimension and comparing the number to a specification, the gauge itself is made to the specification limit. If the part fits, it is within limit; if it does not fit, it is beyond limit. The part either passes or fails with no number involved.
This is called attribute gauging as opposed to variable gauging. A micrometer gives a variable measurement (a number). A go/no-go gauge gives an attribute (pass or fail). Each has its place.
The beauty of attribute gauging is that the result is binary and operator-independent. Any operator who can feel the difference between "enters smoothly" and "does not enter" can perform the inspection correctly on their first attempt.
Go End and No-Go End — The Two-Part Principle
Every complete limit gauge has two working surfaces: the Go member and the No-Go member. They serve different functions and must both pass for the part to be accepted.
| Member | Japanese | Made to | Purpose | Pass condition |
|---|---|---|---|---|
| Go | 通り側 | Maximum Material Limit (MML) | Checks that the hole is not too small (or shaft not too large) | Must enter freely |
| No-Go | 止まり側 | Minimum Material Limit (LML) | Checks that the hole is not too large (or shaft not too small) | Must NOT enter |
For a hole with specification ø10.2 to ø10.4mm: the Go plug is made to ø10.2mm (must pass if hole ≥ 10.2), and the No-Go plug is made to ø10.4mm (must not pass if hole ≤ 10.4). A hole that passes Go but stops No-Go is confirmed within tolerance.
Gauge Tolerance — The Gauge Must Also Have a Tolerance
The gauge itself is not perfectly exact — it also has a manufacturing tolerance. Where this tolerance falls relative to the product tolerance determines whether the gauge system tends to accept borderline non-conforming parts (gauges biased towards product) or reject borderline conforming parts (gauges biased towards gauge).
The most common design rule is the 10:1 rule: gauge tolerance should not exceed 10% of product tolerance. For a 0.2mm product tolerance, gauge manufacturing tolerance should be within ±0.01mm.
In practice, gauge makers follow national standards (JIS B 7420 in Japan, ISO 1938 internationally) that specify both gauge tolerance and wear allowance for plug and ring gauges. The gauge calibration certificate records the actual manufactured size, which is used when the gauge is received.
Types of Go/No-Go Gauges
| Type | Checks | Common application |
|---|---|---|
| Plug gauge (栓ゲージ) | Internal diameter (holes) | Drilled holes, bored features, threaded holes (thread plug gauge) |
| Ring gauge (リングゲージ) | External diameter (shafts) | Turned shafts, pins, cylindrical features |
| Gap / Snap gauge (隙間ゲージ) | External dimension (non-round) | Flats, widths, thickness — faster to use than a ring gauge on shafts |
| Thread plug gauge (ネジ通り止まりゲージ) | Internal thread | Checks thread pitch, form, and minor diameter simultaneously |
| Thread ring gauge | External thread | Bolts, studs, threaded shafts |
| Taper gauge | Taper angle and size | Morse taper holes, cone seats |
When to Use Go/No-Go vs. Variable Measurement
Go/no-go gauges are the right choice for high-volume production inspection where the only required information is pass/fail, the tolerance is not extremely tight (gauge manufacturing is practical), and consistency between operators is more important than knowing the actual value.
Variable measurement (micrometer, CMM, air gauge) is required when you need to know how much deviation exists (for SPC charts, trend analysis, process adjustment), when the tolerance is too tight for practical gauge manufacturing at 10:1 ratio, or when multiple characteristics must be measured and the results combined.
Need pass/fail, high volume, consistent between operators → Go/No-Go
Need variable data, SPC, or tolerance < 0.02mm → Micrometer / CMM
Need both → 100% attribute inspection + periodic variable sampling
Gauge Wear and Calibration
Go gauges wear with use — the Go end is inserted into holes repeatedly and the contact surface gradually wears away. A worn Go gauge becomes smaller (for a plug gauge), which means it will eventually accept holes that are too small. This is exactly backwards from what you want: a worn go gauge produces false passes.
Calibration intervals must be established based on usage frequency and the criticality of the characteristic. The standard approach in Japanese factories: new plug gauges are measured on receipt and the actual size recorded on a calibration certificate. They are re-measured at defined intervals (often monthly for high-use gauges). The Go gauge is condemned when it has worn below the low limit of the gauge tolerance band; the No-Go gauge is condemned if it has grown beyond the high limit.
In practice, No-Go gauges rarely wear significantly because they are only pressed against a surface briefly when the part fails — unlike Go gauges which are inserted thousands of times. Watch the Go end.
寸法公差の上限・下限を物理的に体現した検査治工具。通り側（Go端）は最大実体限界に、止まり側（No-Go端）は最小実体限界に製作される。計量値を読まずに合否を判定するため検査員の技量差がなく高速大量検査に適している。JIS B 7420（プレーン限界ゲージ）、JIS B 0255（ねじゲージ）等で規格化されている。
The Question Every Gauge User Should Ask
Before relying on a go/no-go gauge, ask: "When was this gauge last calibrated and what did it measure?" An undated gauge with no calibration certificate is not a quality tool — it is a prop. The physical form of the gauge guarantees nothing without evidence that it was made correctly and has not worn beyond its tolerance.
A gauge calibration system does not need to be complex. A simple card on each gauge showing its ID number, nominal size, calibration date, next due date, and the measured actual size is sufficient. The discipline to maintain that card is the entire quality system for attribute gauging.