8 3/4 Refurb Question

Hey all, I've started to refurb a 8 3/4 housing I've had lying around for a while. I banged out all the studs and twisted off the brake line vent/tee, next I'm gunna sandblast the outside and paint it. Question is, is this piece in the axle tube supposed to stay in or is it removable/replaceable? What's it called? Pic included.

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