The Solarbotics RW2 rubber wheel has a black, anodized aluminum hub with a generously thick silicone rubber tire for maximum traction (great for minisumo robots or fast line-following robots that need traction when rounding corners).
The rubber tire has a diameter of 1.1 inches (28 mm) and a width of 0.67 inches (17 mm), and it has a 20D durometer. The aluminum hub is drilled for an 3 mm axle. Secure the wheel to your motor shaft with the included 4-40 hex set screw (requires a 0.050-inch hex wrench). The wheel assembly weighs 12 grams. If you are looking to shave some width off your robot design, consider the Solarbotics RW2i wheel, which is a similar design with but has an internal set screw.