I have no idea what this is part of or how used, was in a box lot.  The dome is just over 2" across the bottom and inside are about 3/4" of very fine threads.  Top arm has course threads and screws into the top about an inch.  Also note small bolt and nut on the side which can close the bottom of the dome slightly.  My only thought is that the top arm adjusts pressure level on something.

I think it is a old car hub puller.

You might be right, as I remember, the hubcaps on some old cars screwed on and the threads were very fine and close together.  So, if you removed the hubcap, screwed this item on and then turned the handle it would push the hub off.

I got this one!

its a hub puller for the rear axle of a model T

I have a couple to list on ebay in the morning