covers come in 2 shapes of cavities, so depending on that, is the kind of filter you have to buy.
1 of them is same thickness, the other has a step, so half is higher than the other.
so 1st you need to open the cover and find out the shape: if same thickness, or with step.
if you try to press the wrong 1 in place you may let the air flow straight through the duct without getting filtered.
or you smash the filter badly and same thing happens.
then, you need to find an add that shows clearly that shape..
and some adds dont specify if the price is for 1 or 2-and you need 2.
sometimes the illustrations show 2 but when you get the package you get 1.
so be careful.