just cut slots in the liner but then it dawned on me that the tire would throw water, mud and debris into the slots. So I came up with these. I believe the ones Coz has are stainless where mine are aluminum. Mine also have screen on the backside to help keep junk out. I don't know if the other do or not. I actually developed these on my own. After I showed them to another tt.net member he sent me a link to the ones Coz has.