Blade Install

I have a Black and Decker "Lawn Hog" electric mower model MM875 which I am working to change the blade on. Several months back with some perseverance and a lot of PB Blaster I was able to get the retaining nut to finally break free and remove the old and what looks like original blade. I have ordered a replacement blade but with a new and wet weather system scheduled to arrive Wednesday night I would like to re-install the old blade and pick up as many leaves as I can before the rain arrives. I am reversing the order in which I removed the old blade which is the hard plastic blade dampener,the blade,the square metal spacer and finally the retaining nut. The shaft spins when I try to tighten the nut even when I hold the blade static.



Any advice is appreciated.



Thanks to all.