The other 2 zeros are the ones you already had after defaults.
umask=0 sets 777 permissions for the entire filesystem.
actually it should be umask = 000 (3 octal digits)
If you're familiar with the linux file permissions you know that 777 makes the file rwx (readable, writable and executable) for user group and other. When you mount a vfat filesystem with umask=000 you get the inverse permissions for the files - 777.
It's kinda strange but that's the way it is.
Hope you understand, if you don't you should something about the linux filesystem permissions.