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A door handle is an attached object or mechanism used to manually open or close a door. In the United States, a door handle generally can refer to any fixed or lever-operated door latch device, including on car doors. The term door knob (or simply doorknob) tends to refer to round operating mechanisms.
The traditional door knob has a bolt or spindle running through it that sits just above a cylinder, to which the spindle is connected. Turning the knob pulls the cylinder in the direction of the turn. The end of the cylinder is the latch bolt (more simply known as the latch), which protrudes into a space carved out of the door frame, and which prevents the door from being opened if the knob is not turned. A spring or similar mechanism causes the latch to return to its protruding state whenever the knob is not being turned. Escutcheon plates are the keyhole covers, usually circular, through which keys pass to enter the lock body. If the door handles have a square or rectangular plate on which the handle is mounted this is called the backplate. The backplate can be plain (for use with latches), pierced for keyholes (for use with locks), or pierced and fitted with turn knobs and releases (for use with bathroom locks). The plate on the front edge of the lock where the latch bolt protrudes is called the faceplate.
Door handles can be and have been made out of a wide variety of materials. Just a few examples include brass, white porcelain, brown mineral, cut glass, wood, and victorian bronze. 
Applications and usage
The location of the door handle along the horizontal axis on the door may vary between a few inches or centimeters away from the edge of the door to the exact center of the door, depending on local culture, decorative style or owner preference. The distance from the edge of the door to the center of the handle is called the backset.
The location of the door handle along the vertical axis on the door may vary between 34 inches (864 mm) and 48 inches (1219 mm).
In Europe door levers are more common than the door knob, while in the US, door knobs are traditionally preferred over door levers. However door knobs can be difficult for the young and elderly to operate. For this reason, door handles in most American commercial and industrial buildings and in many households use a lever-operated handle, rather than a knob, as the lever does not require a tight grip. Levers are also beneficial on doors with narrow stile widths where the reduced backset leaves insufficient space to comfortably turn a door knob.
Most household door handles use a simple mechanism with a screw-style axle (called a spindle) that has at least one flat side, which is passed through the door jigger, leaving some length exposed on each side of the door to which the handles are attached. Some handles are attached on both sides by screwing or sliding them directly onto the spindle, and then securing one or more retaining screws (set screws) through the knob perpendicular to the flat of the spindle. Handles that lose traction can frequently be repaired by replacing or adjusting the set screw, which prevents them from slipping on the spindle. Other types of handles, typically used in Europe, slide onto the spindle but are affixed only to the door itself without use of set screws.
Types of household handles:
- Entrance: These door handles are typically used on exterior doors, and include keyed cylinders.
- Privacy: Typically used on bedrooms and bathrooms; while they are lockable (unlockable with a generic tool), they do not have keyed cylinders.
- Passage: Also known as hall or closet, these do not lock and are used in hall or closet doors.
- Dummy: These types are used for ball catch doors or other applications where a mechanism is not needed, but a similar aesthetic effect is desired.
Car door handles
Car door handles may protrude from the vehicle's exterior surface or be streamlined into the vehicle's contour. In some automobiles, especially luxury vehicles, the door handles may feature a key-less entry pad utilizing either a numerical code or thumb scan.
Foldable door handle
On a balcony whose door has an outside shutter, a special door handle is used on the outer side. The protruding part of such handle (usually ring-shaped) can be folded sideways, so that the shutter can be fully closed without being obstructed by the door handle.
Pocket Door Handle
Door handles can also be called "handle sets". In addition there are door handles that are flush-mount and require pressing rather than turning or gripping, and there are touch-free, electronic, and motion-sensor door handles.
Of concern is the fact that door handles are instrumental in the spread of many infections. However, some materials, e.g. brass, copper and silver, are slowly poisonous to many germs. The exact mechanism is not known, but is commonly thought to be via the oligodynamic effect, perhaps by some other electrostatic effect. Brass and copper, for example, disinfect themselves of many germs within eight hours. Other materials such as glass, porcelain, stainless steel and aluminium do not have this effect. Self-disinfecting door handles are particularly important in hospitals, but useful in any building.
Outside door handle of a 1998 Lincoln Town Car, featuring digital lock.
Outside door handle of a 1996 Lancia Y, hidden on the B pillar.
Door latch at Madingley Hall, Cambridgeshire
Ornate door handle on a Moravian Church.
A door handle in the center of a door in Paris
Head shaped doorknob, Florence
A Tulip Schlage doorknob
"Crash bar" handle installed on a glass exterior door
Door handles designed by Ferdinand Kramer, 1925
Flush pull handle Sklo+Glas for sliding glass door
- "Doorknob". Dictionary.com. Retrieved 2008-04-28.
- "Doors". nygate.com. Retrieved 2015-02-28.
- "Infectious diseases". MayoClinic.com. 2011-07-20. Retrieved 2012-09-24.
- "Journal of Materials Science: Materials in Medicine, Volume 19, Number 9". SpringerLink. Retrieved 2012-09-24.
- "BrassversusStainless Steel". Members.vol.at. Retrieved 2012-09-24.
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