This is a simple case fan cover for a PC case with a vent on the top for a top mounted fan. This is meant to stop any dirt or dust from easily getting into your case. I have made sizes that can be used to cover a case that has slots for a 120 and 140 mm fan. The cover is aligned by using the holes that the fan screws into, and the sizes indicate what size fan mount the pegs will fit in to. So for example, if you have a 120mm fan installed but the case supports up to 140mm, you use the 140mm cover. If you have a 140mm fan installed but your case has holes for a 120mm, you use the 120mm cover. You don't have to remove the fan from the case, unless your case only supports one size of fan. This model is also nice if you don't use a fan on the top of your case, as you can stop dust from going inside. If you have any questions or want changes to the model let me know.