This is a 40mm fan mount meant to be mounted on the bolt(s) that connect the extruder block to the X-Carriage on the MakerGear Prusa and is meant to be inline with the X tracks.There are a variation of different versions that have different angles that the fan will mount with.  I personally prefer the 90 degree version.(Note: The pictures posted are actually of an older version of this design, but still retains the same concept)