1Ideal for RC Model Car Boat: 3 joint universal shaft coupler, which is used to connect two shafts and can be bent at any angle, can be used in various model cars and model boats. 2Flexible 3 Joint: A 3 joint universal coupling connector is more flexible than a 2 joint one. The transmission angle is increased, more flexible alignment. 3Durable Steel: Made of 45 # steel with heating and electroplating process, this universal joint coupling is firm and insulating, and make the impact shaft more stable. 44mm to 4mm: The coupling is great for connect your motor of 4mm shaft.The length is 51.5mm / 2.0in, diameter is 12mm / 0.5in, side hole diameter is 3mm / 0.1in. 5Easy To Install and Replace: Ideal replacement accessories for RC model cars and model boats. 3pcs in total, meet your replacement needs.