Dependant on the length of the bore there are various ways, bore micrometers,bore clocks(diatest for smaller bores like this) or CMM.

Other choices include an optical comparator or a microscope with an attached camera (use a scale to measure magnification if unknown).

Hello Pohbah & Corypad,
Many thanks to the quick response. In fact, I've tried it out with a three-pin micrometer but when the accuracy (per the manufacturer specs) is approx. 0.002mm, I don't know if this is fine when the accuracy of the measuring instrument is 20% of the overall tolerance called for the work piece.

Secondly, about the optical comparator, some vendors used to approach me to suggest their sub-micron accuracy scope system, and I believe this could be one of the best option but only when cost is not an issue.

Is that possible to special made a plug-gauge (go-nogo)? What should be the appropriate diameters then?

Thank you in advance.

look at air gauges at this site: http://www.edmundsgages.com/products/airgaging.htm