Plug Gauges are used for checking holes of many different shapes and sizes.
- There are plug gauges for straight cylindrical holes, tapered, threaded square and splined holes.
- At one end, it has a plug of minimum limit size, the ‘GO’ end and; at the other end a plug of maximum limit, the ‘NOGO’ end.
- Snap gauges are used for checking external dimensions. Shafts are mainly checked by snap gauges.
- Thread gauges are used to check the pitch diameter of the thread.
Here the question has about the measurement done by plug gauge, in reality, it just checks the dimension limits. Since it is an official question so we cannot change the language of the question and accordingly best possible answer is cylindrical bores.