The allowed upper and lower gages of a test specimen can be compared with a limit gauge.
It is checked, if the actual dimension of a test specimen is within a tolerance of a requested nominal dimension.
In contrast to the measurements with a caliper or a micrometer, there is no numerical value given.
There is only the statement, if the dimension of the test specimen is good or not.
A big advantage of the limit gauge is the cheap price, compared to e.g. a three-point inside micrometer.
So the limit gauge is very good to figure out if a part is good or needs to be rejected, or if post-treatment is necessary.