Hint W10 - Micro wheels
A further type of wheel is based on the 18mm hub, which is available in a number of colours, and supports a variety of different tyres.
The hub can be either attached onto the end of a Micro K'NEX rod
.. or it can be attached onto the end of a classic K'NEX rod.
Whichever type of rod is used, the hub will spin freely on the end of that rod.