Here is my fan duct for version 5 of the E3D hotend.
To assemble this press the hotend firmly into the extruder. The heater block should be oriented with the heater cartridge facing away from the 40 mm duct. This is not the orientation depicted in the E3D assembly guide but it positions the heater cartridge away from the 40 mm duct and minimizes warping. You will need an 15mm M3 bolt attach the duct to the extruder.
I printed this using a 0.4 mm nozzle, infill 40%, layer 0,2mm, from ABS and PLA.