This dummy motors are used to attach wheel just like a real motor. Use them where you don't need powered wheels. For example in a four wheel (car like) robot you can use two motors at the back which power to the robot while you can attach 2 non-powered wheels on the front using the dummy motor. This Free Wheel shaft comes in handy when you want supporting wheel to your vehicle chassis. It has standard 6mm Shaft diameter and a hole for wheel coupling on shaft rod.