Chapter-7 GO and NOGO Gauge

Plain Plug Gauge

Plug gauge is used for assessment of hole or diameter of an object. With specified tolerance of GO and NOGO side, plug gauge is also known as pin gauge.

Behalf of checking the diameter plug gauge also use in comparing, setting, calibrating of other gauges.

Plug gauges are available in a variety of tolerance of Metric or British standard.

As shown in figure. let say plug gauge size is 25H7 where H7 stand for tolerance standard(+0.0/+0.27)

so, GO side is 25.00 mm

and NOGO side is 25.270 mm

The easy way of finding GO/NOGO side

Go side of plug gauge is always less in diameter but larger in length. But in the case of NOGO, the diameter of NOGO is always greater than GO side.

Easy measurement by plug gauge just assess by which side of gauge fit in hole.

Snap gauge

Snap gauge is GO and NOGO type gauge. That means snap gauge consist 2 fixed measured distance or gap, one is known as GO and another one is known as NOGO.

GO means your job or workpiece is OK and NOGO means your workpiece is rejected.

In snap gauge, value of GO is always greater than NOGO.

Let set an example,

we have a snap gauge of size

12.500 +/_ 0.050 mm

So our

GO size = 12.550 mm

NOGO size = 12.450 mm

and it is measuring criteria for a work piece.

GO condition

According to snap gauge, 25.55 mm size is acceptable for a workpiece. When we push snap gauge towards the workpiece the only area of GO cover i.e. workpiece is accurate.

NOGO condition

If Snap gauge able to move till NOGO area that means workpiece is undersized.

Snap gauge is usually checked for outer surface, which can easily be observed favorable or not.

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