Universal Aluminum Mounting Hub for 6mm Shaft, 4-40 Holes (2-Pack)
Pololu Robotics & Electronics | A-000000-01547
Universal mounting hub to adapt wheels on your mobile robots
Attach the wheels of your mobile robots on your motors with these mounting hubs in aluminum. These two mounting hubs come packaged with screws and key. It fit over 6mm diameter axes.
Resources for the universal aluminum mounting hub for 6mm shaft