This bargain cooling fin heat sink fits my 36mm in-runner perfectly. Best to buy 2 so you can surround the motor completely this will require cutting or grinding away some material and attaching the halves with high temp adhesive. JB weld glue worked for me. I used this setup in my 90mm EDF and never had any overheating problems running a Turnigy 3656 1900kv motor in a freewing fan on 6S. Motor was undersize running over 1500watts with over 50 flights mosly full power. Highly recommended, very cheap insurance for any 36mm inrunner!