This is an adapter to allow a car compartment filter to a 120mm fan in order to filter intake for a server / house / ... The way I use it is that is is screwed in place in one side and the fan is on the other side of the wall / wood / ... Note : the tolerances for the filter are so small you may need a blade or something similar to push the filter in place ( no need to cut anything ). I also recommend printing with no supports.