Interesting topic. I have 3 filters. One came with 6 pack air cleaner and it has the V shaped outer screen with the square nylon mesh inner. I have a hemi air cleaner with the round holes and square mesh (picture), and this new in the box example that looks just like the box picture but oval. V outer and square mesh.

So are all assembly line filters round outer hole, or did the diagonal also come assembly line depending on time frame? Or is the diagonal the over-the-counter part?