Mount for the Ender 3 Pro, may fit other models.  Replaces the cap with the QR code and adds a mounting point for a camera or other accessory.  I mounted the Fiberpunk Sentry Pro to mine using a bolt through the camera mount on the bottom.  Included a hole to route cables/secure with a zip tie.  Printed with 3 walls with the layer lines running along the length of the mounting area for strength.  Tree supports worked fine. V2 is lighter weight and may need some post processing to fit what you are mounting.  V3 is set up a little heavier and has a shorter, wider (6.5) mm slot for a standard camera mount bolt.