Latches are normally in the extended position with an angled or curved edge that causes the latch to be pushed into the door when it contacts the similarly curved edge of the strike in the normal action of closing the door. Turning the knob or lever will also withdraw the latch, allowing the door to be opened. With some locks, operating the key will withdraw the latch without needing to turn the knob or lever. There are two main categories of latches – springlatches and deadlatches.
CYLINDRICAL KNOB AND LATCH
TUBULAR KNOB AND LATCH