Bayonet mount

A bayonet mount

A bayonet mount before and after insertion

A bayonet mount or bayonet connector is a fastening mechanism 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 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.

Uses

This style of connector was named after its original use for soldiers who need to mount bayonets to the ends of their rifles in a hurry. The same need also applies to photographers who may need to change lenses quickly.

Several classes of electrical cable connectors, including audio, video, and data cables use bayonet connectors. Examples include BNC, C, and ST connectors.

Home light bulbs (230/240V mains voltage) in India, Australia, Ireland, New Zealand, the UK, Middle East and, in older installations, France, also have this type of "B" base, as well as the Edison screw "E" base used in the United States, Japan 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 fire. Bayonet cap bulbs are very common worldwide in applications where vibration may loosen conventional bulbs, such as automotive lighting and other small indicators, and in many flashlights.

Some bulbs may have slightly offset lugs to ensure they can be only inserted in one direction; this is particularly true 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 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.

Bulb bayonet mounts

Compact fluorescent lamp with double contact B22d bayonet mount

Incandescent light bulb with double contact B22d bayonet mount, and corresponding socket with sprung connectors

Preceding bulb mounted in the socket

LED lamps with GU10 bi-pin twist-lock mount

Incandescent 40W BA15d bulb

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:^[1]

Of these, only the BC (Ba22d) is commonly sold in supermarkets.

References

1. ^ see http://technical.greenstock.co.uk/KYBLampBases.htm

• IEC 61184: Bayonet lampholders, International Electrotechnical Commission, 1997. (also: BS EN 61184) – specifies requirements and tests for the B15 and B22 bayonet holders for light bulbs used in some Commonwealth countries

See also

• Bipin
• Arri bayonet
• Lens mount
• Joseph Swan
• Bayonet - a type of knife that attaches to a rifle.

External links

• GU-24 Goes Mainstream
• Line-voltage Socket Design Competition (GU24)