best way to measure 8 microns ID 1

[limct]

I'd like to know the best way to measure a diameter 6mm (G6, ie. tolerence +0.004 / +0.012). Thank you.

 

[pohbah]

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

 

[CoryPad]

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

 

[limct]

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.

 

[EdDanzer]

look at air gauges at this site:

http://www.edmundsgages.com/products/airgaging.htm