This big fan duct was designed for large nozzle or dual extruder head. it cool down around the nozzle and its cold part. it's designed for a 40mm fan and it fit well with http://www.thingiverse.com/thing:169844 and Greg's X carriage with fan mount. LED strip can be added see instructions for more infouse the two upper holes to tightned the part between the 40mm fan and the X carriage. glue the lower part of the fan for better rigidity. if the air flow is too intense on the upper openings, use some tape to obstruct them.