The motor shaft is 8mm and has one flat side, but is shown here with a 9mm round shaft to create proper cutaway holes.
This is a model of the Etonm ET-WGM58AE motor used by the Maslow CNC. A schematic for this motor can be found in https://github.com/MaslowCNC/Electronics/tree/master/Documentation/Data%20Sheets
The radius of this is not displayed on the diagram, and is estimated. It should be checked.
Hole of 2.25mm is the recommended clearance bolt hole for a M4 bolt, not the measured hole id for the thread which will be 3.3mm