The black tires are made of soft, spiked rubber for increased traction, and the plastic hubs are chrome (silver) in color.
The included adapters let you easily mount the wheels to motors with 4mm output shafts. These wheels are sold in pairs: you get two wheels, two 4mm adapters, and one 3mm hex wrench that matches the adapter screws.
An included pair of adapters lets you easily mount the wheel to motors with a 4mm output shaft, such as the 25D mm metal gearmotors.
A 3mm hex (or Allen) wrench is included for use with the adapter screws.