Plug Gauges
These are used to check the internal diameter for component. It has two limits, lower is the GO size/OK size where as the higher limit is the No Go condition, if this enters in the hole then it is deduced that the job is not OK.
They are generally assembled from standard parts where the gauge portion is interchangeable with other gauge pieces (obtained from a set of pin type gauge blocks) and a body that uses the collet principle to hold the gauges firmly.