file "60mm_to_40mm_fan_adapter" is a plain 60mm to 40mm reducer.
file "Cetus_60_to_40_Reducer_plus_Dia15H70" is a Cetus (or pp3dp) file with the part combined as you would do in solidworks. It is still printable as one part but it has minor flaws
but no functional flaws. This file contains a cylinder for cooling the main object while printing i.e. the extruder travel to position x and prints a random object to give the detailed part of the main object some extra cooling time.
file "Cetus_60_40_Reduc_V50" is a combined file i.e. one solid object.