I was looking thru the owners manual today and the 2005 Z I just bought says it uses a splined bushing on the mower blades. Exmark said that was new for 2005 1/2 models. What is this spline for? Apparently I'm not going to be able to use my old blades on my new mower if I understand Exmark correctly. I haven't taken the blades off to verify this but I am wondering why this was done. I usually order from J-Thomas but not sure if they would be up to date on this recent change. Any info on whether I can use my old blades or where to order new ones that have the spline bushing would be helpful. Thanks!