What is this part called?

My factory balancer has that part permanently attached to it. I dont believe its intended to be removed or replaced
Thanks Fawkes. Does that mean when someone uses an aftermarket balancer (which don't seem to come with the dust shield, at least mine didn't), they just run it without the dust shield and the large felt donut? I'm sure lots of guys use aftermarket balancers. Is the dust shield and felt donut optional?