I just bought a M3000, and would like to change the shims. Does anyone know what size of the nut in the stock? I don't have a socket that fits and want don't know what size to look for.

I expect you found out long ago but for anyone else wondering the same thing what you need is a 16mm deep reach socket. I have a 16mm extended spark plug socket that does the job nicely. Don't overtighten the stock bolt it needs to be snug but not cranked down supertight.