A latch is a type of mechanical fastener that is used to join two (or more) objects or surfaces together while allowing for the regular or eventual separation of the objects or surfaces.

Note that a latch is not the same as the locking mechanism

Lock (device)

A lock is a mechanical or electronic fastening device that is released by a physical object or secret information , or combination of more than one of these....

 of a door or window, although often they are found together in the same product.

A latch typically engages another piece of hardware on the other mounting surface. Depending upon the type and design of the latch, this engaged bit of hardware may be known as a keeper or strike.

Latches range in complexity from flexible one piece flat springs of metal or plastic, such as are used to keep blow molded plastic power tool cases closed, to multi-point cammed latches used to keep large doors closed.

Spring latch

• Latch bolt: This is an extremely common latch type. Typically part of a lockset
  Lockset
  A lockset or alternatively lock set is the hardware and components that comprise the locking mechanism that can usually be found on a door or other hinged object but can also include sliding doors and dividers....
  
  , it is a spring-loaded bolt with an angled edge. When the door is pushed closed, the angled edge of the latch bolt allows it to retract. Once the door is fully closed, the spring engages and the latch bolt fully extends and holds the door closed. The latch bolt is disengaged (retracted) typically when the user turns the door handle
  Door handle
  A door handle is an attached mechanism used to open or close a door. In the United States, door handle can refer to any fixed or lever-operated door latch device, including on car doors. The term door knob tends to refer to round operating mechanisms.-History:The first documented invention of the...
  
  , which via the lockset's mechanism, manually retracts the latch bolt, allowing the door to open.
• Passage/Privacy
• Deadlatch (entry) includes an extra tongue to prevent shimming
• Deadbolt latch (single throw bolt)
• Spring bolt lock
  Spring bolt lock
  A spring bolt lock, also known as a night latch, is where a locking mechanism is used with a latch bolt.* For information on locks, see Lock * For spring bolt lock used as a latch, see Latch* For comparison of use, see Dead bolt lock...
  
   (or night latch): When a locking mechanism is used with a latch bolt

Slam latch

A slam latch uses a spring and is activated by the shutting or slamming of a door. Like all latches, a slam latch is a mechanism to hold a door closed. The slam latch derives its name from its ability to slam doors and drawers shut without damaging the latch. A slam latch is rugged and ideal for industrial, agricultural and construction applications.

Cam lock

A cam lock is a type of latch consisting of a base and a cam. The base is where the key or tool is used to rotate the cam, which is what does the latching. Cams can be straight or offset; offset cams often are reversible.

Norfolk latch

A Norfolk latch is a type of latch incorporating a simple thumb-actuated lever and commonly used to hold wooden gates and doors closed. In a Norfolk

Norfolk

Norfolk is a low-lying county in the East of England. It has borders with Lincolnshire to the west, Cambridgeshire to the west and southwest and Suffolk to the south. Its northern and eastern boundaries are the North Sea coast and to the north-west the county is bordered by The Wash. The county...

 latch, the handle is fitted to a backplate independently of the thumb piece.

Introduced around 1800–1820, Norfolk latches, originating in the English

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 county

County

A county is a jurisdiction of local government in certain modern nations. Historically in mainland Europe, the original French term, comté, and its equivalents in other languages denoted a jurisdiction under the sovereignty of a count A county is a jurisdiction of local government in certain...

 of the same name, differ from the older Suffolk latch, which lacked a back plate to which the thumbpiece is attached.

Suffolk latch

A Suffolk latch is a type of latch incorporating a simple thumb-actuated lever

Lever

In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...

 and commonly used to hold wooden gates and doors closed.

The Suffolk latch originated in the English county of Suffolk

Suffolk

Suffolk is a non-metropolitan county of historic origin in East Anglia, England. It has borders with Norfolk to the north, Cambridgeshire to the west and Essex to the south. The North Sea lies to the east...

 in the 16th century and stayed in common use until the 19th century. They have recently come back into favour, particularly on garden gates and sheds. They were common from the 17th century to around 1825, and their lack of a back plate made them different from the later, and neighbouring Norfolk latch (introduced 1800–1820). Many of these plates found their way into America and other parts of the world.

Crossbar

A crossbar, sometimes called a bolt, is a primitive fastener consisting simply of a post barring a door

Door

A door is a movable structure used to open and close off an entrance, typically consisting of a panel that swings on hinges or that slides or rotates inside of a space....

. Crossbars are no longer in modern use in the western world.

Crossbars were historically common, simple fasteners consisting simply of a plank or beam mounted to one side of a door by a set of cleats. The board could be slid past the frame to block the door. Alternatively, the bar can be a separate piece that is placed into open cleats or hooks, extending across the frame on both sides. The effect of this device is essentially the opposite of the crash bar

Crash bar

A crash bar is a mechanism for unlatching a door, consisting of a spring-loaded metal bar fixed horizontally to the front of the door and hinged...

 in that its operation is to permit the door to be opened inward rather than outward. On a set of double doors, the same principle works, but needn't extend past the frame. The bar simply extends into another set of cleats on the other door such as to interfere with the door opening.

Cabin hook

A cabin hook is a hooked bar that engages into a staple. The bar is usually attached permanently to a ring or staple

Staple (fastener)

A staple is a type of two-pronged fastener, usually metal, used for joining or binding materials together. Large staples might be used with a hammer or staple gun for masonry, roofing, corrugated boxes and other heavy-duty uses...

 that is fixed with screw

Screw

A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

s or nails to woodwork or a wall at the same level as the eye screw. The eye screw is usually screwed into the adjacent wall or onto the door itself. Used to hold a cupboard

Cupboard

A cupboard or press is a type of cabinet, often made of wood, used indoors to store household objects such as food, crockery, textiles and liquor, and protect them from dust,vermin and dirt....

, door or gate open or shut.

A cabin hook is used in many situations to hold a door open, like on ships to prevent doors from swinging and banging against other woodwork as the ship moves due to wave action. This usage spread also to other domains, where a door was required to be held open or a self-closing device is used to close the door.

Many buildings are built with fire-resistant doors to separate different parts of buildings and to allow people to be protected from fire and smoke. When using a cabin hook in such a situation, one should keep in mind that a fire-resistant door

Fire door

A fire door is a door with a fire-resistance rating used as part of a passive fire protection system to reduce the spread of fire or smoke between compartments and to enable safe egress from a building or structure or ship...

 is an expensive and heavy item, and it only works as a fire door if it is always closed. To open the often heavy fire door easily, magnetic door holders are used that are released when the buildings electrical fire alarm system

Fire alarm system

An automatic fire alarm system is designed to detect the unwanted presence of fire by monitoring environmental changes associated with combustion. In general, a fire alarm system is classified as either automatically actuated, manually actuated, or both...

 is activated by a fire. As cabin hooks must be activated manually, they are inappropriate for fire doors.

Other latches

• Bolt lock latch
• Compression latch
• Draw latch (both over- and under-center)
• Rotary latch

Firearms

Firearms require specialized latches used during loading and firing of the weapon.

A break-action firearm is one whose barrels are hinged and a latch is operated to release the two parts of the weapon to expose the breech and allow loading and unloading of ammunition. It is then closed and re-latched prior to firing. A separate operation may be required for the cocking and latching-open of a hammer to fire the new round. Break open actions are universal in double-barrelled shotguns, double-barrelled rifle

Rifle

A rifle is a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the projectile , imparting spin around an axis corresponding to the...

s and combination gun

Combination gun

A combination gun is a break-action hunting firearm that comprises at least two barrels, a rifle barrel and a shotgun barrel, often but not always in an over and under configuration; side-by-side variations are known as cape guns. A ' refers to a combination gun that has three barrels...

s, and are also common in single shot rifles, pistol

Pistol

When distinguished as a subset of handguns, a pistol is a handgun with a chamber that is integral with the barrel, as opposed to a revolver, wherein the chamber is separate from the barrel as a revolving cylinder. Typically, pistols have an effective range of about 100 feet.-History:The pistol...

s, and shotgun

Shotgun

A shotgun is a firearm that is usually designed to be fired from the shoulder, which uses the energy of a fixed shell to fire a number of small spherical pellets called shot, or a solid projectile called a slug...

s, and can also be found in flare gun

Flare gun

A flare gun is a firearm that launches flares. It is typically used for signalling, as distress signalling, at sea or from the ground to aircraft...

s, grenade launcher

Grenade launcher

A grenade launcher or grenade discharger is a weapon that launches a grenade with more accuracy, higher velocity, and to greater distances than a soldier could throw it by hand....

s, air gun

Air gun

An air gun is a rifle , pistol , or shotgun that fires projectiles by means of compressed air or other gas, in contrast to a firearm, which burns a propellant. Most air guns use metallic projectiles as ammunition. Air guns that only use plastic projectiles are classified as airsoft...

s and some older revolver designs.

Several latch designs have been used for loading revolver

Revolver

A revolver is a repeating firearm that has a cylinder containing multiple chambers and at least one barrel for firing. The first revolver ever made was built by Elisha Collier in 1818. The percussion cap revolver was invented by Samuel Colt in 1836. This weapon became known as the Colt Paterson...

s. In a top-break revolver, the frame is hinged at the bottom front of the cylinder

Cylinder (firearms)

In firearms terminology, the Cylinder refers to the cylindrical, rotating part of a revolver containing multiple cartridge chambers. The cylinder revolves around a central axis in the revolver to bring each individual chamber into alignment with the barrel for firing...

. The frame is in two parts, held together by a latch on the top rear of the cylinder. For a swing out cylinder, the cylinder is mounted on a pivot that is coaxial with the chambers, and the cylinder swings out and down. Some designs, such as the Ruger Super Redhawk

Super Redhawk

The Super Redhawk is a line of double action magnum revolvers made by Sturm, Ruger beginning in 1987, when Ruger started making weapons using larger, more powerful cartridges such as .44 Magnum, .454 Casull, and .480 Ruger.-The introduction:...

 or the Taurus Raging Bull

Taurus Raging Bull

The Raging Bull is a revolver manufactured by the Brazilian Taurus International firearm company.In its larger calibers it is marketed as a hunter's sidearm because it is a potent weapon with plenty of stopping power...

, use a latches at the front and rear of the cylinder to provide a secure bond between cylinder and frame.

To fire a revolver, generally the hammer is first manually cocked and latched into place. The trigger, when pulled, releases the hammer, which fires the round in the chamber.

Knives

Various types of knives with folding or retractable blades rely on latches for their function. A switchblade

Switchblade

A switchblade is a type of knife with a folding or sliding blade contained in the handle which is opened automatically by a spring when a button, lever, or switch on the handle or bolster is activated A switchblade (also known as an automatic knife, pushbutton knife, switch, Sprenger, Springer,...

uses an internal spring to produce the blade which is held in place by a button-activated latch. Likewise a ballistic knife

Ballistic knife

A ballistic knife is a specialized combat knife with a detachable gas- or spring-propelled blade that can be fired to a distance of several feet or meters by pressing a trigger or switch on the handle.-History and usage:...

uses a strong latch to restrain a powerful spring from firing the blade as a projectile until triggered by opening the latch. A gravity knife

Gravity knife

A gravity knife is a knife with a blade contained in its handle, and which opens its blade by the force of inertia or gravity. As the gravity knife requires gravity or inertia to propel the blade out of the handle, it differs fundamentally from the switchblade, which opens its spring-propelled...

relies on a latch to hold the folding blade in an open position once released. A balisong

Balisong (knife)

A Butterfly knife, also known as a fan knife or Balisong, is a folding pocket knife with two handles counter-rotating around the tang such that, when closed, the blade is concealed within grooves in the handles. It is sometimes called a Batangas knife, after the Tagalog province of Batangas in the...

uses a single latch to hold the folding blade both open and closed, depending on the position of the handles; by rotating 180 degrees the same latch can be used in either configuration. Balisong latches have numerous variations, including magnetic variants and some which can be opened via a spring when the handles are squeezed together.

Utility knives

Utility knife

A utility knife is a knife used for general or utility purposes. The utility knife was originally a fixed blade knife with a cutting edge suitable for general work such as cutting hides and cordage, scraping hides, butchering animals, cleaning fish, and other tasks.Today, the term "utility knife"...

also often use a latch to hold a folding knife both open and closed. This allows it to be locked in orientation to the handle when in use, but also safely stowed otherwise. To open a knife of this type may require significantly more force than the weapons variety as an added safety feature.

Other

Crossbows incorporate a type of latch to hold the drawn bowstring prior to firing.

Automobiles

Automobiles incorporate numerous special purpose latches as components of the doors, hood/bonnet

Hood (vehicle)

The hood or bonnet is the hinged cover over the engine of motor vehicles that allows access to the engine compartment for maintenance and repair. In British terminology, hood refers to a fabric cover over the passenger compartment of the car...

, trunk/boot

Trunk (automobile)

The trunk or boot of an automobile or car is the vehicle's main storage, luggage, or cargo compartment. Trunk is used in North American English and Jamaican English; boot is used elsewhere in the English speaking world. Trunk is also primarily used in many non-English speaking regions, such as...

, tailgate

Tailgate

Tailgate is an American English word denoting the door or 'gate' at the back of a wagon, pickup truck, SUV or other similar type of vehicle that is hinged at the bottom and can be opened for the convenience in loading cargo into the rear of the vehicle...

, seat belt

Seat belt

A seat belt or seatbelt, sometimes called a safety belt, is a safety harness designed to secure the occupant of a vehicle against harmful movement that may result from a collision or a sudden stop...

s, etc.

On passenger cars, a hood may be held down by a concealed latch. On race cars or cars with aftermarket hoods (that do not use the factory latch system) the hood may be held down by hood pins.

The term Nader bolt is a nickname for the bolt on vehicles that allows a hinged door to remain safely latched and closed. It is named after consumer rights advocate and politician Ralph Nader

Ralph Nader

Ralph Nader is an American political activist, as well as an author, lecturer, and attorney. Areas of particular concern to Nader include consumer protection, humanitarianism, environmentalism, and democratic government....

, who in 1965 released the book Unsafe at Any Speed

Unsafe at Any Speed

Unsafe at Any Speed: The Designed-In Dangers of the American Automobile by Ralph Nader, published in 1965, is a book detailing resistance by car manufacturers to the introduction of safety features, like seat belts, and their general reluctance to spend money on improving safety...

 which claimed that American cars were fundamentally flawed with respect to operator safety.

Latches in seatbelts typically fasten the belt which constrains the occupant to the body of the car. Particularly in rear seats slightly different latches may be used for each seat in order to prevent the seatbelts from being attached to the wrong point. Inertial seatbelt release is a potential circumstance where, in a collision, the seatbelt latch can unintentionally come loose leading to potential injury of the passenger. An additional risk of seatbelt latches is that in some cases the occupant may believe the latch is secure (e.g., by hearing a characteristic click) when in fact it has not.