A latch mechanism is the canister that's pushed via the border of the door. This can also be referred to as a tubular latch mechanism. The mechanism includes a spring-loaded latch which retracts to open the door and upon the launch of this Door Knob or lever, protrudes to keep the door closed.
A knob is usually a round shape that's used to catch with your hands and open a doorway. Knobs are made from aluminum, zinc die-cast or other products.