These wheels are great for robotics, custom RC vehicles, or any other project you need to get rolling. They measure 60 mm (2.36″) in diameter and are designed to press-fit securely onto D output shafts with a diameter of 3 mm. They are compatible with many of our gearmotors, including our micro metal gearmotors and our mini plastic gearmotors. Two mounting holes for #4 or M3 screws make it possible to use the wheel with any of our universal mounting hubs for those screw sizes, enabling these wheels to be used with our larger metal gearmotors and stepper motors. The slots in the five spokes fit #2 or M2 screws and allow additional accessories to be mounted to the wheel such as decorations or parts of an encoder system.