cartridge mounting ? for clearaudio

a few kind of dummy questions here:
the clearaudio aurum classic that i have came with a bag of standard mounting screws, and was also attached to its box with a set of plastic mounting screws. are those just for the presentation of the package? or would one want to use those to mount the cartidge?

this cart. seems to be threaded, and does not need nuts to fasten it to the tonearm? should i be using nuts anyways to secure it?

along with the mounting hardward came a little metal plate, that would seem to go inbetween my cart and tonearm. is this to adjust overall mass? or change the height of the cart? i've never seen something like this before and there is no mention of it in my setup manual.