Stihl FS91R Weed Trimmer Head Change To Metal Blade 

Mine was the same, had to get both kits 4180 007 1032 and 4180 007 1013. 1032 for the deflector shield, 1013 for the washer, nut, and cone to be able to tighten and be secure. Problem I was having was the cone part from the 1032 kit would be loose because that washer around the splined part in the middle; it was like the washer on the bottom of it was too far down and wouldn't let the nut tighten against the cone, it was only tightening against the middle splined piece. Kinda annoying having to get 2 kits but oh well.