Flywheel nut question

[joey11]

I bought an 03 EC 250 Dealer Edition a year or so ago and have ridden the heck out of it since. This was my first real enduro bike, and now that I'm getting faster, I think I want a little more snap. I opened up my ignition cover yesterday and to my surprise, there was a FWW added by the previous owner. I thought everything was stock. I took the weight off, and I want to try the bike this way, as I am sure it will liven it up. The problem is that I don't have a nut to put back on the crank bolt. Does this matter? It this nut a special piece? It appears the nut would have threads on the outside and on the inside to thread on to the crank bolt. I also am guessing that I will need a thin walled socket (FWW took a 22mm) to get it tight. Any help would be great.