5 Lug conversion question

[niss]

I recently purchased some used Z32 rear hubs for my 5 lug conversion. When I recieved them I noticed a little washer type thing on the back side of them. 1 of the hubs had one and the other seems to be missing it. Is this something that I can take off of a 4 lug hub and replace onto the Z32 hub? Is this piece really neccessary? Any info would be greatly appreciated. Thanks in advance.

[the head]

i would venture a guess that it is a grease seal of some sort but teh best way to know is to pull one of your rear hubs if it has it move one over if it dosent take teh other one out