This is an extrusion cooling fan mount for a MakerBot Replicator 2X. It requires a blower fan such as the one found on the Replciator 2. This works a bit too well - it can push so much air across hot plastic that it can distort the plastic. Also beware its tendency to cool the hotends a bit, even though its airflow isn't aimed at the heater. Print it out of ABS, so it doesn't warp from radiant heating near the hotends. This makes cooling/printing PLA on the 2X a breeze.