A mechanical or hinged fastener used to allow movement between two surfaces, like opening and shutting, is known as a latch. They can be simple mechanical devices or a complex system of several latches combining to form a more complicated latching format. They can be worked with spring action, by the movement of plastic or metal springs or when the door or locking surface shuts. The rotary latch is operated by a key which turns the latch into the open or shut position. There are several other variations of these simple latches, like crossbars, etc which are used in various other applications.
Latches were traditionally made of metal but contemporary latches are made of other light weight materials such as plastics which, in combination with metallic parts, makes the latch sturdy, functional and less heavy and cumbersome.
One type of commonly-used plastic latch is the automobile door latch. Automobile doors are constantly opened and shut and the latch is the snap-shut type, which undergoes extensive wear and tear. The door has to snap shut and remain securely latched to prevent the door from opening by itself and posing a hazard to life. The latch must be durable, hardy and lightweight enough to withstand cracking from repeated impact, very high and low temperature variations, hence these latches are made of tough, yet flexible plastic compounds and shaped by injection molding process. One-way latches are commonly used in office automation equipment like copy machines, projection machines, etc and these small, yet useful latches keep the equipment covered and free of dust and debris.
Plastic with metal insert latches are also used in refrigerators, where the plastic latch has a metal strike and catch with magnetic qualities to allow the door to be closed automatically.
Washing machines and dryers also have plastic latches which are molded and may have small metal inserts to catch and snap shut, to make the washing and drying operation safe while the machine is running. These latches may also have child-proof locking systems for additional safety.
Another common plastic latch is the non-locking type which can be used for interior doors, screen doors, baths and office cabins. The locking mechanism may be separate from the latch. Trailers or campers may also have plastic door latches with locks on their entrance doors.
Hinged, flip-type plastic latches are commonly found on baggage-doors inside aircraft, buses, trains etc where the hinged door needs to snap shut and stay securely in place. These doors are usually light-weight, but they may be subject to strain by the movement of the vehicle, hence the latch must be very strong and sturdy.