What are the dimensions of a technic axle?
I found CAD files for LEGO technic axles here: https://grabcad.com/library/lego-technic-axles-1
and some gears which have holes for technic axles here: https://grabcad.com/library/lego-technic-gears-1
Using their online viewer I found the following dimensions (Which are a little inaccurate due to the limits of their online viewers tools. For more accurate and detailed dimensions download a copy of the CAD files)


This would seem to indicate (if accurate) an interference fit between the outsides of the axles and the holes (i.e. the hole is slightly smaller) which could be accurate as axles are usually tight.
Someone should also probably measure actual LEGO parts with some calipers for confirmation on these dimensions.