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?