This fan duct is designed to mount 30mm layercooling fans directly onto the stock e3d-v6 fan duct that clips onto the heatsink.
Mirror the part if you want dual layercooling fans.
edit: added source files in SW2015 and STEP. But beware, i did not design this fanduct with customization in mind so these files are rather a quick and dirty solution i'm not proud of ;-)
Mirror the part for printing a second fan duct if you wish dual layercooling fans.