You guys are gonna love this. Yesterday, I was sharpening all of my blades and I was trying to decide which one to put on my 20" trim mower. I thought about the doubles issue and looked it over. Hey, why not try it? It's a 5.5 b&s and it worked great. The governor won't allow high rpm but it worked anyway. One of the blades was the original mulching blade and the other was a rather flat blade. I put the flat blade on the bottom. I'm gonna reverse it next time to see which way works best. I use it for more than trim on a couple of lawns which is why I wanted to try it.