Plug gauges are the limit gauges for a hole and consists of two cylindrical wear-resisting steel plugs whose sizes are made to the limiting values of the hole dimension. The plug made to the lower limit of the hole is known as "GO" gauge, and this will obviously enter any hole which is not smaller than the lower limit allowed. The plug made to the upper limit is known as "NOT-GO" or "NO-GO" gauge, and will not enter any hole which is smaller than the upper limit allowed. GO and NO-GO plugs are arranged at either end of a common handle.

In progressive plug gauges both the "GO" and "NO-GO" gauges are on the same side separated by a small distance. First the GO portion is inserted into the hole. After the full length enters into the hole, further entry will be obstructed by the portion if NO-GO of the hole is within the tolerance limits.

Plain ring gauges are used to check the outside diameter of cylindrical parts.
Separate gauges are used for checking ‘Go’ and ‘No- Go’ sizes.
A `No-Go’ gauge is identified by an annular groove on the knurled surface.

Taper plug gauges are used to check tapered holes. It has two check lines. One is a GO line and another is a NOGO line. During the checking of work, NOGO line remains outside the hole and GO line remains inside the hole.

These gauges made with standard or special tapers are used to check the size of the hole and the accuracy of the taper. The gauge must slide into the hole for a prescribed depth and fit perfectly. An incorrect taper is evidenced by a wobble between the plug gauge and the hole.

Gauge is an inspection tool used to check product dimension with reference to its maximum and minimum acceptable limits. It is, generally, used to segregate acceptable and non-acceptable products in mass production, without the exact dimensions. It is made of tool steel and is heat treated.