Understanding Go and No-Go Gauges

Go and No-Go gauges are used to check the tolerance level of manufactured pieces in mass production.
They are designed to provide a rapid pass/fail test for component dimensions, reducing the time needed to take precise measurements for every piece made.

Types of Go and No-Go Gauges

Plug Gauge

A plug gauge is a cylindrical tool used to check the conformity of drilled or milled holes.
These are typically double-ended, with a ‘Go’ end that should freely insert into the hole, and a ‘No-Go’ end that should not.

Snap Gauge

A snap gauge is used for checking external dimensions including the diameters of workpieces such as shafts.
It has two ‘Go’ anvils on one end that should slip over the workpiece, and two ‘No-Go’ anvils on the other end that should not.

Ring Gauge

A ring gauge is used to verify the dimensions of cylindrical objects. A ‘Go’ ring should slide onto the workpiece, while a ‘No-Go’ ring should not.

To use a Go and No-Go gauge, the workpiece is first checked with the ‘Go’ end. If the ‘Go’ end fits, then the piece should be within the minimum permissible size.
The ‘No-Go’ end is then tried. If it doesn’t fit, then the piece should be within the maximum permissible size.
If the workpiece fails either the ‘Go’ or the ‘No-Go’ test, it is outside the tolerances set for that dimension, and classified as defective.

Despite their simplicity, these gauges need to be handled with care. A forceful attempt to insert a ‘No-Go’ gauge can damage the gauge and the workpiece being checked.
Always clean the tool and workpiece before testing. Dirt or debris can cause false readings.
The rigidity and quality of the gauge material is also important, as these factors can affect the accuracy of the test.
It should be noted that these gauges only provide a binary pass/fail result and do not give detail on how close the part is to the upper or lower limit of the tolerance range.