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A hinge is a mechanical bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation, with all other translations or rotations prevented; thus a hinge has one degree of freedom. Hinges may be made of flexible material or moving components. In biology, many joints function as hinges, such as the elbow joint.

Ancient remains of stone, marble, wood, and bronze hinges have been found. Some date back to at least Ancient Egypt, although it is nearly impossible pinpoint exactly where and when the first hinges were used.^[1]

In Ancient Rome, hinges were called cardō and gave name to the goddess Cardea and the main street Cardo. This name cardō lives on figuratively today as "the chief thing (on which something turns or depends)" in words such as cardinal.^[2]

According to the OED, the English word hinge is related to hang.^[3]

Barrel hinge

A barrel hinge consists of a sectional barrel (the knuckle) secured by a pivot. A barrel is simply a hollow cylinder. The vast majority of hinges operate on the barrel principle.^[4]

Butt hinge / Mortise hinge

Any hinge designed to be set into a door frame and/or door is considered a butt hinge or mortise hinge. A hinge can also be made as a half-mortise, where only one half is mortised and the other is not. Most mortise hinges are also barrel hinges because of how they pivot (i.e., a pair of leaves secured to each other by knuckles through which runs a pin).^[5]

Butterfly / Parliament (UK) hinge

A decorative variety of barrel hinge with leaves somewhat resembling the wings of a butterfly.

Case hinge

Similar to butt hinges, but usually more decorative; most commonly used in suitcases, briefcases, and the like.

Concealed hinge

Used for furniture doors (with or without a self-closing features and/or damping systems), they consist of two parts: (1.) the cup and arm, and (2.) the mounting plate. They are also called "cup hinges", or "Euro hinges", as they were developed in Europe and use metric installation standards. Most concealed hinges offer the advantage of full in situ adjustability for standoff distance from the cabinet face, as well as pitch and roll by means of two screws on each hinge.

Continuous / Piano hinge

This variety of barrel hinge runs the entire length of a door, panel, box, etc. They are manufactured with or without holes.

Flag hinge

A simple two-part hinge, where a single leaf, attached to a pin, is inserted into a leaf with a hole. This allows the hinged objects to be easily removed (such as removable doors). They are made in right- and left-hand configurations.^[6]

H hinge

These H-shaped barrel hinges are used on flush-mounted doors. Small H hinges (3–4 in or 76–102 mm) tend to be used for cabinets, while larger ones (6–7 in or 150–180 mm) are for passage doors and closet doors.

HL hinge

Commonly used for passage doors, room doors, and closet doors in the 17th, 18th, and the 19th centuries. On taller doors, H hinges were occasionally used between them.

Pivot hinge

This hinge pivots in openings in the floor and the top of the door frame. Also referred to as double-acting floor hinges, they are found in ancient dry stone buildings and, rarely, in old wooden buildings. They are a low-cost alternative for use with lightweight doors.^[7] Doors with these hinges may be called haar-hung doors.

Self-closing hinge

This is a spring-loaded hinge with a speed control function. The same as spring hinge, usually use spring to provide force to close the door and provide a mechanical or hydraulic damper to control door close speed. That can prevent door slamming problem while auto closes a door.^[8]

Spring hinge

A spring-loaded hinge that provides assistance in closing or opening the hinge leaves. An inner spring applies force to keep the hinge closed or opened.^[9]

Swing Clear hinge

Also called offset door hinges, they are ideal for residential and commercial doors, they allow doors to swing completely clear of their openings.^[10] They can easily comply with Fair Housing Act (FHA) code by providing a minimum ADA 32” clearance when using a 34” door slab.^[11]

Living hinge

A hinge of flexible plastic that creates a join between two objects without any knuckles or pins. Molded as a single piece, they never rust or squeak, and have several other advantages over other hinges, but are more susceptible to breakage.^[12]

Other types of hinges include:

• Coach
• Counter Flap
• Cranked or storm-proof
• Double action non-spring
• Double action spring
• Flush
• Friction
• Lift-off
• Pinge (with a quick-release pin)
• Rising butt
• Security
• Tee

Since at least medieval times, there have been hinges to draw bridges for defensive purposes for fortified buildings. Hinges are used in contemporary architecture where building settlement can be expected over the life of the building. For example, the Dakin Building in Brisbane, California, was designed with its entrance ramp on a large hinge to allow settlement of the building built on piles over bay mud. This device was effective until October 2006, when it was replaced due to damage and excessive ramp slope.

Hinges appear in large structures such as elevated freeway and railroad viaducts, to reduce or eliminate the transfer of bending stresses between structural components, typically in an effort to reduce sensitivity to earthquakes. The primary reason for using a hinge, rather than a simpler device such as a slide, is to prevent the separation of adjacent components. When no bending stresses are transmitted across the hinge, it is called a zero moment hinge.

A variety of self-actuating, self-locking hinges have been developed for spacecraft deployable structures such as solar array panels, synthetic aperture radar antennas, booms, radiators, etc.^[13]

Pin

The rod that holds the leaves together, inside the knuckle. Also known as a pintle.

Knuckle

The hollow—typically circular—portion creating the joint of the hinge through which the pin is set. The knuckles of either leaf typically alternate and interlock with the pin passing through all of them. (aka. loop, joint, node or curl)

Leaf

The portions (typically two) that extend laterally from the knuckle and typically revolve around the pin.

End play

Axial movement between the leaves along the axis of the pin. This motion allows the leaves to rotate without binding and is determined by the typical distance between knuckles (knuckle gap) when both edges of the leaves are aligned.

Gauge

Thickness of the leaves.

Hinge width

Length from the outer edge of one leaf to the outer edge of the other leaf, perpendicularly across the pin (aka open width).

Hinge length

The length of the leaves parallel to the pin.

Knuckle length

The typical length of an individual knuckle parallel to the pin.

Leaf width

Length from the center of the pin to the outer edge of the leaf.

Pitch

Distance from the end of a knuckle to the same edge of its adjacent knuckle on the same leaf

Door Stop

A colloquialism referring to loose angular movement of the leaves relative to the pin.^[14]

Butler tray hinge

Folds to 90 degrees and also snaps flat. They are for tables that have a tray top for serving.

Card table hinge

Mortised into edge of antique or reproduction card tables and allow the top to fold onto itself.

Carpentier joint

A hinge consisting of several thin metal strips of curved cross section.

Drop-leaf table hinge

Mounted under the surface of a table with leaves that drop down. They are most commonly used with rule joints.

Hinged expansion joint

an expansion joint with hinges that allow the unit to bend in a single plane

Hinged handcuffs

a restraint device designed to secure an individual's wrists in proximity to each other consisting of two cuffs linked with a double or triple hinge. Hinged handcuffs cuffs tend to restrict movement more than chain-linked handcuffs, and they can be used to generate more leverage to force a suspect's hands behind the back, or to apply pain against the wrist, forcing the subject to comply and stop resisting.^[15]

Hinge region

portion of antibody structure between the fragment antigen-binding region and the fragment crystallizable region

Living hinge

a hinge consisting of material that flexes

Piano hinge

(or coffin hinge) a long hinge, originally used for piano lids, but now used in many other applications where a long hinge is needed.

• 
  Old construction of hinges in the dry stone wall near Bignasco.
• 
  Ancient pivot hinges, found in the dry stone buildings.
• 
  A flushed door hinge.
• 
  A barrel hinge made of wrought iron.
• 
  A barrel hinge made of bronze strap.
• 
  Increasing the number of loops to 3 allows the butt hinge axis to be fixed from both ends.
• 
  Door in furniture with spring to lock door both fully shut and fully open positions. It hides completely behind the door and has adjustment for fine alignment. Allows the door to open even when against a wall.
• 
  Rusty hinges on a building exterior.
• 
  This door hinges on the stile and is called a haar-hung door.
• 
  A living hinge on the lid of a Tic Tac box.
• 
  Hinged handcuffs
• 
  A piano hinge.
• 
  A continuous hinge.
• 
  Swing Clear Hinge
• 
  Hinge on the Sydney Harbour Bridge. It was used during construction of the bridge and now accommodates thermal expansion and contraction of the bridge

• Hinge bender, a tool for adjusting hinges
• Concealed hinge jig – Support and locating tool for drilling recess holes to mount concealed hinges
• Floating hinge – Type of hinge that allows rotation and some linear movement
• Geared continuous hinge – Type of continuous hinge used mostly on doors in high-traffic entrances
• Plain bearing – Simplest type of bearing, with no rolling elements
• Hinge joint, a skeletal bone joint functioning like a hinge

• Hinge Terminology—Hingecraft; graphics visualizing many terms
• Guden Hinges and Industrial Hardware: Glossary