I've got some of those Toro 2-Cycle 21"s... I bought Gator Blades the other day, and when I replaced my OEM blade setup there was this 6-7" piece with the blade as well. Looked like it was something to do with the mulching system or something. Anyways, I didn't put it back on. What is it? And should it be on there with the Gators?