Most HVAC air filters are usually slightly undersized from stated dimensions by about 1/4" or so. These filters are exact size, or in some cases oversized by about 1/8". I was able to modify them to fit and they will work, but I recommend paying very close attention to nominal and actual size listing, and comparing to your actual size vent, when placing an order.
I have 2 A/C units at my house. One has a standard, easy to find filter size and the other one is an impossible to find size. After hearing the ads that stated they carry hard to find sizes, I decided to give them a try. I am glad I did. Not only did I find the size I needed, but I was able to sign up for auto ship. We live in a rural area so this was a real plus. The filters arrived super fast and fit perfectly. Highly recommend!