This heat sink is a professional and practical heatsink , fit for 540 550 and 3650 size motor , it will come with a 5V cooling fan , This cooling fan can power up from the receiver , to protect your motor. very easy to use . Keep motors cool , Make your electric motor run more efficiently by keeping it cooler. Heat is the killer of electrical components especially motors if you keep them cooler they will perform better and last longer.This heat sink will help to do that. Parts Name : Heat Sink with 5V cooling fanMaterial : Aluminum Alloy + Hard PlasticColor : PurpleInside Diameter : 34.6 mmFan size : 30x30x10 mmThickness : 2 mmWeight : 21.5gQty: 1 pcs The dimensions are measured manually, so the deviations may exists, hope you can understand us and thank you very much !! Welcome to our store. Please do not hesitate to contact us if you have any questions or concerns before or after your purchase, we will reply to you within 24 hours. Thank you very much! Please feel free to contact us if you have any issue or need further assistance, we are here for you. Please check your specific model's manual for compatibility.