The official measurement per the prints is 1.630".
What you (or any given individual) measure with a comparator insert may or may not jive with that, as they (the comparators) are intended for a relative measurement, not absolute. Case in point: my Forster GO gauge is marked 1.630", but with my Stoney Point insert (which as a radiused edge to the hole) it measures closer to 1.624-1.625".