A customizable 30mm fan guard, blanking plate, shim, and/or duct.  Print with zero top/bottom layers and use infill to create grating for a fan guard.  Print solid to blank a fan opening.  Print with multiple perimeters and zero infill to use as a 2mm shim (spacer).   The ‘z-scalable’ STL has the top & bottom chamfers removed, making it suitable for slicer z-scaling to create shims/ducts of any desired thickness/length.  Experiment and enjoy!

[edit]  Holes are 3.2mm close-fit clearance for M3 screws.