The NW-75 Wall Cover Inlet is a two piece cover that includes a base plate and cover. This allows you to install the base plate and seal it to the wall before installing your line set. The cover is then installed after your line set. The NY-75 Simple Wall Cover does not include a base plate. This makes it more difficult to achieve a weather-proof seal between the wall and cover. I recommend the NW-75 because it will be easier to ensure that your line is fully protected from the elements.
This also applies to all other sizes of the line-hide wall covers.