I had some stuff hard Anodised and it came out great except a couple of reamed holes had reduced in size!
Dimensional changes can vary depending on which anodising process was used!
Whereas plating is purely additive, anodising is a conversion of the surface layer. The layer is formed by consumption of the surface aluminium to fuel the growth of the aluminium oxide matrix, and typically the thickness of the resultant layer is about double the amount of substrate consumed. Growing a 1 thou layer will have typically consumed 0.5 thou of the underlying part so every surface will now be 0.5 thou bigger - so if you anodise a part all over to a 1 thou layer, outside dimensions will be 1 thou bigger and the actual bore diameter of a hole will be 1 thou smaller.
Anodising to take colour usually uses sulphuric acid electrolyte (known as Type II anodising). For lighter/brighter colours which benefit from light being reflected from the underlying aluminium, 0.5 thou ano layer is often about right. To get black parts, you need to ano to a full 1 thou layer to get enough of those big black molecules into the dye matrix to block out all of the light.
"Hard" anodising can take several forms. Type IIB is basically just the same as a thin, undyed Type II but at a reduced temperature; Type III is again the same as Type II but much thicker - maybe up to 5 thou - and needs near-freezing electrolyte. Type I hard-coat anodising on the other hand uses chromic acid and builds a far denser, thinner layer which can be as little as 1/4 or 1/2 a thou thick.
So, if your "hard coat" was produced by Type I anodising, the reduction in bore might have been as little as 0.25 thou - but if it was Type III anodised the bore could have reduced by 5 thou.
If you have dimensionally-critical parts, it isn't just the actual anodising that needs to be considered. Anodising needs perfect electrical contact between the electrolyte and the whole surface so, after degreasing, parts almost always have some form of etch dip to remove the random oxide layer that has formed by exposure to atmospheric oxygen. This is a purely consumption process, so makes parts smaller; and if over-done can (a) reduce dimensions, and (b) reduce surface quality.
So, usually anodising gives you a slightly bigger part - but not always!