Top quality materials: Aluminum shell (case) High quality magnets Copper wires of high temperature endurance Top quality bearings Dustproof design. Built-in temperature sensor. When the temperature of the motor is higher than a factory-preset value, the speed controller will stop the motor automatically. (This function is only available when using Hobbywing's speed controller.) 8.5T to 21.5T motors use low resistance 3.5mm bullet-connectors, easy for installation (Plug and play) The sensor port of 8.5T to 21.5T motors is parallel to the end bell, easy for installation, more suitable for smaller chassis with limited space.