This robot wheel is designed to work with the Digilent SRK(Servo-Robot-Kit). It has a D connector in the center. It is also designed to be used with an O-ring. This provides traction for the SRK.

Print two of the wheels at full scale. Fit an O-ring in the groove of each wheel. Slide it onto the D-connector. It is designed to be a tight fit.

Attribution - Creative Commons

Digilent, MRK, Robot, wheel, oring, Dconnector