E3D-v6 Fan Duct for Threaded mount

The standard e3d fan duct doesn't work very well with the threaded mount version of the heatsink because the fan can come into contact with either the mounting surface (effector, etc) or the heater block. This version of the fan does not extend above the upper mounting flange of the heatsink and also does not go below the top of the heater block, so this is no longer a potential issue.