Features: 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 34-38mm. The 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 designed clamp shape and exquisite workmanship, the heatsink is durable for long term use. Specifications: Item name: Heatsink Cooling Fan with Thermal Sensor Fan input: 5-10V Fan size: 30 x 60mm Clamp suitable for: 540 550 3650 3660 Motors Weight: 42g : Metal colour: blue Package Contents: 1 x Heatsink Cooling Fan with Thermal Sensor Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the a little different from the real thing. The measurement allowed error is +/- 1-3cm.