In hubbing, a male hub (master) is created with a profile that will form an impression on the female piece. The male hub is generally hardened and the female die block softened by annealing to help form the impression. As the metal flows the face of the die block is deformed, and, generally, must be machined flat. The die block is often a cylinder that is reinforced with a surrounding steel ring during the hubbing process. Hubbing is usually less expensive than die sinking, i.e., machining the female die, and multiple dies can be made from the male hub.