GO and NOGO Gauge

Dec 13, 2025

Deepak Choudhary

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Plain Plug Gauge

A plain plug gauge is used to check the diameter of a hole. It works on the GO and NO GO principle and is also commonly called a pin gauge.

Apart from checking hole diameter, plug gauges are also used for comparison, setting, and calibration of other gauges.

Plug gauges are manufactured according to standard tolerances, such as Metric or British standards.

Example

Assume a plug gauge size of 25 H7.

Important correction:
For 25 H7, the tolerance is +0 / +0.021 mm (not +0.27 mm).

So:

GO side = 25.000 mm
NO GO side = 25.021 mm

Identifying GO and NO GO Sides

The GO side has a smaller diameter and longer length.
The NO GO side has a slightly larger diameter and shorter length.

Measurement Using a Plug Gauge

Measurement is done by checking which side of the gauge fits into the hole:

If the GO side enters fully and the NO GO side does not, the hole is within tolerance.
If the NO GO side also enters, the hole is oversized.

Snap Gauge

A snap gauge is also a GO–NO GO type gauge. It consists of two fixed gaps:

One gap represents the GO limit
The other represents the NO GO limit
GO → Workpiece is acceptable
NO GO → Workpiece is rejected

For external measurements, the GO size is always larger than the NO GO size.

Example

Let the snap gauge size be:

12.500 ± 0.050 mm

Then:

GO size = 12.550 mm
NO GO size = 12.450 mm

This becomes the acceptance criterion for the workpiece.

GO Condition

If the snap gauge passes over the workpiece only up to the GO side, the workpiece is within tolerance and accepted.

NO GO Condition

If the snap gauge passes through the NO GO side, the workpiece is undersized and rejected.

Application

Snap gauges are mainly used for checking external dimensions, where acceptance or rejection can be quickly and visually confirmed.

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