I add that people must rely on real facts not what measures are listed , they are a "general view". So for example for Size 8 wikipedia lists 8.14 yet in CAD software the designer must take in account the polishing factor of 0.1-2 and this must be checked with calliper on a real life product in order to get used with the manufacturer error pool.
Other than that I add that Size 8 US fits my ring finger on left hand and I`m a "medium man" and right handed , on the right hand I have bigger size.
So fellow designers first prototype and measure in real life on plastics then on a real final product to get the experience on the manufacturing part.
I know it can be tedious , but once you learn it ...
Don`t jump in sending straight "Gs" and get prepared to call hospital if you fit a smaller ring size on the fat finger , or have at hand a dremel cutting tool and tech friends ... just in case!
And big note : get your rings out your fingers when you sleep or work involving tools ... imagine the finger going fat when you sleep due some medical condition like : flue , bad temperatures , and stuff