Do you feel confidence in your testing of the bore diameter before anodize and the process controls in place when the part is fabricated?  Yes there are gages accurate enough to measure the part but doing it up front is only part of your battle.

Holding such tolerances on an anodized part is notoriously difficult.  The etching portion of the procedure removes material and then the anodizing is supposed to build it back by a similar amoung.  Differences in bath quality, time, surface preparation, and raw stock quality all affect the result.

Does this feature need to be anodized or could it be added afterward?  Adding it afterward could save you a bunch of trouble.

Regards,

Here is a gauge I recommend:

http://www.defelsko.com/pt6kFR.html

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

What instrument are you using to measure the bore prior to the anodizing process?

What is the basic bore dimensions?

Here is a listing of a variety of coating thickness gauges:
http://www.reliabilitydirect.com/ultrasoundproducts/thicknessindex.htm

Anodizing involves the electrolytic oxidation of a surface to produce a tightly adherent oxide scale which is thicker than the naturally occurring film. I suggest your designers fix the thickness of the anodized layer they calculate to meet its service requirements, and machine the bore to give a slightly greater than finished size which will then be brought down to the required diameter by the anodizing process. Do not forget that whatever the thickness of the layer your plater/processor will produce, you will need to allow for double that as you will be dealing with a diameter (i.e two times radius.