The most common limit gage used for inspecting the hole diameter is

The correct option is Plug gage.

To understand why this is the correct answer, let's look at the function of each gage listed in the options:
1. Plug gage: A plug gage is a limit gage used to check the accuracy of holes. It has two ends, a "Go" end and a "No-Go" end, which are designed to verify if the diameter of the hole falls within the specified tolerance limits.
2. Ring gage: A ring gage is used to check the external diameter of a cylindrical object, such as a shaft or bolt.
3. Snap gage: A snap gage is a quick checking limit gage used to inspect external dimensions, such as thickness, width, or external diameters.
4. Master gage: A master gage is a reference gage used primarily for calibrating other gages, rather than direct inspection of workpieces.

Therefore, for inspecting the hole diameter, the most common limit gage used is the Plug gage.