There's been some interesting and helpful discussion here so far, but I'd like to inject a word about bore gauges in general, which is just to say that unless you really need to know something about the interior shape of a hole, it's best to avoid using them. They are have notorious repeatability--and often reproducibility--problems, and require a good deal of experience and development of "feel" in order to be used with confidence. Not only that; often the actual measurement values are not as important as just discerning the lack of cylindricity present in the hole. If consistent shape is important, to a certain degree actual size may not be as critical.
In short, never use a bore gage when a pin will do.
In short, never use a bore gage when a pin will do.