These blue plastic wheels have silicone tires and measure 70 mm (2.75″) in diameter, and they press-fit onto 3mm D shafts, such as those on our micro metal 小短文h啪纯肉+办公室. 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.