These yellow plastic wheels have silicone tires and measure 80 mm (3.15″) in diameter, and they press-fit onto the 3mm D shafts on many of our motors, including our micro metal gearmotors and our mini plastic gearmotors. Additionally, this wheel is compatible with several of our universal mounting hubs, which can serve as adapters for motors with different shafts. This product is a pair of wheels.