Rear Speed controller for the Nanrobot D4+ 2.0 (New Generation) and D4+ 3.0 Scooters. Each sold separately. To determine if you need this part or a different Scooter, check your wheels for "RoadRunner Scooter" engraved on the wheels. If there is an engravement, order this Scooter. Please contact RoadRunner Scooters for assistance.