Many K'NEX sets include Racing wheels. These are available in three hub types:
1. Hub Racing wheel 37mm.
2. Hub Racing wheel 50mm.
3. Hub Narrow 50mm.
The Hub Racing wheel 37mm and the Hub Racing wheel 50mm may be fitted with a tyre if required.
There are two types of tyre available for the Hub Racing wheel 37mm - tyres with tread (as shown) or tyres without tread ("slick" tyres).
A further alternative is to fit one or more Connector 8-way White into a Tyre Racing wheel 37mm, so as to form a tyred wheel.
The Hub Narrow 50mm can be fitted inside a Tyre Narrow Black.
Alternatively, two of the hubs can be fitted inside a Tyre Racing wheel 50mm, as shown in the photo.
Racing wheel hubs run freely on the end of a classic K'NEX rod, whereas the narrow hub runs freely on a rod pushed through the hole in the hub's centre, as shown in the photo.
If you want the rod and wheel to turn at the same time, please view Hint W6.