Wheel hexes, sometimes known as hubs, are often used to connect an RC car's axles to its wheels. (See image at right.)
On many cars, there are optional hexes available with different widths, allowing you to change the track width of the car.
Some kits come with plastic hexes but then have aluminum hexes available as option parts for durability.
Some kits also have optional lightened hexes to reduce weight in the drivetrain.