Robot wheel for 4mm shaft with flat

This design is part of a differential drive robot. The wheels are approximately 78mm in diameter. The wheel can directly couple to a 4mm ‘D’ shaft, where the flat spot is 3.5mm across from the width of the shaft. 

The wheel can be used as is printed in PLA or PETG. An optional non slip tyre printed from FLEX can be used to improve grip. The tyre will slip the existing tread and hold in place.

The photos show it printed in 0.2mm PLA. If over-extrusion is negatively impacting the ability to fit the shaft into the hub or m3 nuts for the screws, then I suggest using variable layers to add more resolution to the hub.

Details of the motor seen in the photos is can be found at https://www.dfrobot.com/product-1617.html