Hub/ brakes

[Srjustin]

I put new axles hubs welded diff and breakes iny s13. Well in the back theres a duster cover ( thin round pieace of metal so im guessing some sort of dust cover) i for got to put it in and it goes on be4 the hub. Do i need it? I was told it doesnt do anything Lol but i want other opinions.

Thanx guys!