This heat sink fit for 540 550 and 3650 size motor , to protect your motor. very easy to use . Compatible with most traxxas , HSP , tamiya . and losi electric motors . 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 do that. Parts Number : 03300Parts Name : Heat SinkMaterial : Aluminum Alloy Color : PurpleInside Diameter : 34.6 mmHeight : 28 mmThickness : 2 mmWeight : 21 gQty: 2 pcs