This RC motor heat sink is specially designed for 540 550 3650 3660 motors of RC model car.It fit the motor which diameter is 34-38mmThe RC heat sink with thermal sensor is equipped with 5-10V cooling fan to protect your motor.The thermal sensor will accurately detect rising temperature, when the motor is up to 40, the cooling fan will automatically turn on to cool the motor.The cooling fan can be powered up from the receiver, convenient and easy to use. With high quality material designed clamp shape and exquisite workmanship, the heatsink is durable for long term use.Specifications:Item name: Heatsink Cooling Fan with Thermal SensorFan input: 5-10VFan size: 30 x 60mmClamp suitable for: 540 550 3650 3660 MotorsColour: BlackMaterial: composite materialPackage Contents:2 x Motor Heatsink Cooling FanOnly the above package content, other products are not included.Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.