In most situations of manufacturing it is impractical to pull out the a dial caliper and check every dimension on manufactured parts. So specialized tools such as the plug go-no-go gage, ring go-no-go gage and the snap go-no-go gage were created to increase productivity in quality control.
The plug gages are used to check whether hole diameters are within their specified tolerances. With the plug go-no-go gage one end of the gage is made to fit through a hole being measured which is called the go-gage and the other end is made not to fit the dimension or is called the no-go gage. A progressive type of plug go-no-go gage has the go and no go diameters on the same side.
Ring gages are used for measuring external our outside diameters. The go-no-go ring gages work off of the same idea as the plug go-no-go gages in that one side of the ring gage is GO, where the part should fit, and the other side is called the NO GO, where the part should not fit.
Snap Gages serve the same purpose as the ring go-no-go gages except that they are adjustable and can check the size of both internal and external diameters.