Floor Mandrel
From DT Online
The Blacksmith's Floor Mandrel is a large, floor standing Cast Iron cone around which rings and hoops can be formed and trued up after welding.
Most are hollow and some have a slot down the side to provide clearance for Tongs gripping the hot metal.
Most Blacksmiths would be able to form rings on the Bick of the Anvil and true them by eye, so a Floor Mandrel is more common in a Wheelwright's workshops where hoops and rings are made on a daily basis..