This is one of the most popular types of rear wheel and sprocket with drive belt found on Chinese made children's electric scooters. It is compatible with models such as the Ro4. Specifications: Width: 83 mm / 3.27 inches Diameter: 136.84 mm / 5.39 inches Bearing Hole Size: 8 mm / 0.31 inches Outer Diameter of Belt Sprocket: 82 mm / 3.23 inches This part is suitable for electric scooters with 120w and 24v power systems.