This fan mount just clips on the inside of the lower frame of a 2020 aluminium Kossel Mini (in my case a Folger Tech kit). I use three of these clips to have some air movement over the tower stepper motors in order to keep them cool.
Each fan is mounted on the rail about 0.5-1 inch away from the stepper motor and blowing over the side and rear. This keeps the stepper motors nice and cool, whereas before I would have failed prints due to overheating motors.
To me this is an essential upgrade for any (FolgerTech) kossel!
Mount fan with 12mm M3 bolts and nuts.