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Bayonet mount

Bayonet mount

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A bayonet mount or bayonet connector is a fastening mechanism
A fastener is a hardware device that mechanically joins or affixes two or more objects together.Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container,...

 consisting of a male side with one or more pins, and a female receptor with matching L slots and spring(s) to keep the two parts locked together.

To couple the two parts, the pin(s) on the male are aligned with the slot(s) on the female and the two pushed together. Once the pins reach the bottom of the slot, the two parts are turned in opposite directions to guide the pin across the bottom of the L shaped slot. The spring then holds the pin in position to prevent it from backing out. To disconnect, the two parts are pushed together to overcome the spring whilst twisting slightly to reverse the locking turn.

The strength of the joint relies on the shear strength
Shear strength
Shear strength in engineering is a term used to describe the strength of a material or component against the type of yield or structural failure where the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a material along a plane that is...

 of the pins and the strength of the L slots which hold the pins in place when locked. A practised user can connect them quickly and they are not subject to cross-threading.


This style of connector was named after its original use for soldiers who need to mount bayonet
A bayonet is a knife, dagger, sword, or spike-shaped weapon designed to fit in, on, over or underneath the muzzle of a rifle, musket or similar weapon, effectively turning the gun into a spear...

s to the ends of their 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 in a hurry.

In camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...

s with interchangeable lenses
Photographic lens
A camera lens is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.While in principle a simple convex lens will suffice, in...

, the bayonet-style lens mount
Lens mount
A lens mount is an interface — mechanical and often also electrical — between a photographic camera body and a lens. It is confined to cameras where the body allows interchangeable lenses, most usually the single lens reflex type or any movie camera of 16 mm or higher gauge...

 likewise allows the photographer to quickly change lenses. The bayonet-style mount additionally allows for the precise alignment of mechanical and electrical connections between modern camera bodies and lenses. Camera lens mounts usually employ stronger flattened tabs rather than pins, though their function is the same.

Bayonet connectors are employed for use in electronic, electrical power, control circuits and to supply a physical connection between to cables transmitting any kind of impuls, signal, audio or electronic data. The bayonet connectors are derived from the threaded series to provide faster coupling and anti-vibration resistance. The coupling system is usually made of 3 bayonet ramps machined on the external side of the receptacle connector and 3 stainless steel studs mounted inside the plug connector’s coupling nut.Several classes of electrical cable connectors, including audio
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

, video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...

, and data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...

A cable is two or more wires running side by side and bonded, twisted or braided together to form a single assembly. In mechanics cables, otherwise known as wire ropes, are used for lifting, hauling and towing or conveying force through tension. In electrical engineering cables are used to carry...

s use bayonet connectors. Examples include BNC
BNC connector
The BNC connector ' is a common type of RF connector used for coaxial cable. It is used with radio, television, and other radio-frequency electronic equipment, test instruments, video signals, and was once a popular computer network connector. BNC connectors are made to match the characteristic...

, C
C connector
The C connector is a type of RF connector used for terminating coaxial cable. Coupling uses two-stud bayonet-type locks. The C connector was invented by Amphenol engineer Carl Concelman. It is weatherproof without being overly bulky....

, and ST connectors.

Many types of light bulbs also employ bayonet connectors.

Bulb bayonet mounts

The bayonet light bulb mount is still prevalent in many former members of the British Empire
British Empire
The British Empire comprised the dominions, colonies, protectorates, mandates and other territories ruled or administered by the United Kingdom. It originated with the overseas colonies and trading posts established by England in the late 16th and early 17th centuries. At its height, it was the...

 such as India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, Ireland
Republic of Ireland
Ireland , described as the Republic of Ireland , is a sovereign state in Europe occupying approximately five-sixths of the island of the same name. Its capital is Dublin. Ireland, which had a population of 4.58 million in 2011, is a constitutional republic governed as a parliamentary democracy,...

, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

, the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 as well as regions of the Middle East
Middle East
The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...

. Older installations in countries like France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 also have this type of B base, as well as the Edison screw
Edison screw
The Edison screw fitting is a system of connectors used for light bulbs, developed by Thomas Edison and licensed starting in 1909 under the Mazda trademark. Most have a right-hand threading, so that it goes in when turned clockwise and comes out when turned counterclockwise, like a hardware screw...

 (E) base used in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

 and other countries. These bulbs have two pins on opposite sides of the cap; however, some specialized bulbs have three pins (cap designation B22d-3) to prevent use in domestic light fittings. Examples of three pin bulbs are found in mercury street lamps and fireglow bulbs in some older models of electric radiative heater. Bayonet cap bulbs are very common worldwide in applications where vibration may loosen conventional bulbs, such as automotive lighting
Automotive lighting
The lighting system of a motor vehicle consists of lighting and signalling devices mounted or integrated to the front, sides, rear, and in some cases the top of the motor vehicle...

 and other small indicators, and in many flashlight
A flashlight is a hand-held electric-powered light source. Usually the light source is a small incandescent lightbulb or light-emitting diode...


Some bulbs may have slightly offset lugs to ensure they can be only inserted in one orientation; this is case in bulbs like the 1157 automobile tail-light which has two different filaments to act as both a running light and a signal light. In the 1157 automotive bulb, each filament has a different brightness and is connected to a separate contact on the bottom of the base, the two contacts being symmetrically positioned about the axis of the base (unlike a 3-way medium screw base in which the two filament contacts are a center circle and a ring,) so proper orientation of the bulb is necessary to connect each filament to the correct separate circuit. Newer bulbs use a wedge base
Wedge base
A wedge base is a type of electrical connector used as a fitting for small light bulbs. It is similar to the bi-pin connector, except that the two "pins" are the same wires that extend into the bulb , and the wires are bent up onto the sides of the base, where they make contact with the socket...

 which does not have this issue.

Bayonet bases or caps are often abbreviated to BC, often with a number after. The number refers to the diameter of the base (e.g., BC22 is a 22 mm diameter bayonet cap lamp). BC15, a 15 mm base, can also be referred to as SBC standing for small bayonet cap. The lowercase letter s or d refers to whether there are one (single) or two (double) contacts on the bottom of the bulb.
Type IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...

DIN or Din or din can have several meanings:* A din is a loud noise.* Dīn, an Arabic term meaning "religion" or "way of life".* Din is one of the ten aspects of the Ein Sof in Kabbalah ....

Ansi is a village in Kaarma Parish, Saare County, on the island of Saaremaa, Estonia....

B15d IEC 60061-1 (7004-11) DIN 49721
BA15d IEC 7004-11 A DIN 49720
BA15s IEC 7004-11 A DIN 49720
BA20d IEC 7004-12 DIN 49730
B22d IEC 60061-1 (7004-10)
GU10 IEC 60061-1 (7004-121)
GZ10 IEC 60061-1 (7004-120)
GU24 Pending (Mar 2007)

While G actually indicates bi-pin, those listed above have a twist-lock, but with parallel pins from the end instead of opposing pins on the side.

These are the available sizes in the UK:
Designation Alternative designation Contacts Dimension, etc.
BA5s 1 5 mm
BA7s 1 7 mm
BAX9s 1 9 mm
BA9s Miniature bayonet cap (MBC) 1 9 mm
BA15d Small bayonet cap (SBC) 2 15 mm
BAX15s 1 15 mm
BA15s Single centre contact (SCC) 1 15 mm
BA20s 1 20 mm
BA20d 2 20 mm
BA21d 2 21 mm
B21-4 21 mm 4 pin
BA22d Bayonet cap (BC) 2 22 mm
BC-3 Bayonet cap (BC) 2 22 mm 3 bayonet pins
B22d-3 2 22 mm double ended (railway)
BX22d 2 22 mm

Of these, only the BC (BA22d) is widely used in homes.

See also

  • Edison screw
    Edison screw
    The Edison screw fitting is a system of connectors used for light bulbs, developed by Thomas Edison and licensed starting in 1909 under the Mazda trademark. Most have a right-hand threading, so that it goes in when turned clockwise and comes out when turned counterclockwise, like a hardware screw...

  • Bipin
    A bipin or bi-pin, , is a standard from the IEC for lamp fittings. These are used on many small incandescent light bulbs , and on most fluorescent lights as well, where the filaments are involved in starting the tube when it is turned on.Some lamps have pins placed closer together, preventing...

  • Arri bayonet
    Arri bayonet
    Arri bayonet is a lens mount developed by Arri for use with both 16 mm and 35 mm movie camera lenses. Lenses of this type are distinguished by "outer wings" which both control aperture and bayonet alignment, and are placed in the mount while two pressure tabs are simultaneously depressed at the...

  • Joseph Swan
    Joseph Swan
    Sir Joseph Wilson Swan was a British physicist and chemist, most famous for the invention of the incandescent light bulb for which he received the first patent in 1878...

  • Bayonet
    A bayonet is a knife, dagger, sword, or spike-shaped weapon designed to fit in, on, over or underneath the muzzle of a rifle, musket or similar weapon, effectively turning the gun into a spear...

    – a type of knife that attaches to a rifle.

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