Wedge base
A wedge base is a type of electrical connector
Electrical connector
An electrical connector is an electro-mechanical device for joining electrical circuits as an interface using a mechanical assembly. The connection may be temporary, as for portable equipment, require a tool for assembly and removal, or serve as a permanent electrical joint between two wires or...

 used as a fitting for small light bulbs. It is similar to the bi-pin connector, except that the two "pins" are the same wire
A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...

s that extend into the bulb (rather than being rigid), and the wires are bent up onto the sides of the base, where they make contact with the socket. The wires are usually inserted into a plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

 base that the bulb is mounted in, and which is often narrower at the tip than at the bulb, giving it a wedge
Wedge may refer to:Mathematics:* Triangular prism, a parallel triangle wedge* Wedge , a polyhedral solid defined by two triangles and three trapezoid faces* Wedge product, a mathematical term, named for the ∧ operator symbol used...

 shape and usually ensuring a tight connection, depending on manufacturing
Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...

Tolerance (engineering)
Engineering tolerance is the permissible limit or limits of variation in# a physical dimension,# a measured value or physical property of a material, manufactured object, system, or service,# other measured values ....

s. Some bulbs have no plastic base, and the wires are simply bent up to the sides of the bulb's glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...


The bulb is inserted and removed with straight in or out force, without turning as with a bayonet mount
Bayonet mount
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 to keep the two parts locked together....

 or 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...

, on certain bi-pin light sockets. For true wedges, compression is the force that holds the bulb in, while others use simple friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

, or snap into a socket with spring
Leaf spring
Originally called laminated or carriage spring, a leaf spring is a simple form of spring, commonly used for the suspension in wheeled vehicles...

-loaded electrical contacts that "grab" the corners or other protrusions on the base to prevent loosening from vibration
Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...


Bulbs of this type are commonly used in 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 in low-voltage lighting used in landscape lighting. The bulb may have dual filaments, acting as both a low-wattage tail light or parking light and a higher-wattage brake light or turn signal. In this case, one has its contacts near the center of the base, and the other toward the outside edges, so that they cannot be accidentally swapped. Along with putting contacts on the opposite (alternating) sides, this gives the base rotational symmetry
Rotational symmetry
Generally speaking, an object with rotational symmetry is an object that looks the same after a certain amount of rotation. An object may have more than one rotational symmetry; for instance, if reflections or turning it over are not counted, the triskelion appearing on the Isle of Man's flag has...

 so that the user does not have to determine the exact position of the bulb before inserting a new one.

Wedge bases are designated with the letter W and possibly a second letter indicating the exact type (often keyed to prevent the wrong colors from being used in automobiles), the thickness in millimetres, a lowercase x, the width in millimeters, and a lowercase d to indicate a double-contact (single-filament) bulb or q for a quad-contact (dual-filament) one. Like small bi-pins, the measurement may be expressed as a decimal, such as 2.5, instead of a whole number
Whole number
Whole number is a term with inconsistent definitions by different authors. All distinguish whole numbers from fractions and numbers with fractional parts.Whole numbers may refer to:*natural numbers in sense — the positive integers...


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 bulbs are also made that will retrofit
Retrofitting refers to the addition of new technology or features to older systems.* power plant retrofit, improving power plant efficiency / increasing output / reducing emissions...

 incandescents with the same base, but may affect the electrical relay that controls the blinking of turn signals, or cause others sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...

s to assume that a light bulb is out (see idiot light
Idiot light
A tell-tale is an indicator of the status or malfunction of a system within a motor vehicle. Tell-tales consist of a light bulb or an LED which lights up a symbol or text legend...

). In this type of "bulb", all of the LEDs may light regardless of which of the contacts are activated on the base, but like a dimmer
Dimmers are devices used to vary the brightness of a light. By decreasing or increasing the RMS voltage and, hence, the mean power to the lamp, it is possible to vary the intensity of the light output...

 or a three-way screw-in fluorescent, the brightness
Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target...

 is changed instead by the bulb's internal electronic
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...


Although several types of fixture
Light fixture
A light fixture, light fitting, or luminaire is an electrical device used to create artificial light and/or illumination, by use of an electric lamp...

Electrical ballast
An electrical ballast is a device intended to limit the amount of current in an electric circuit. A familiar and widely used example is the inductive ballast used in fluorescent lamps, to limit the current through the tube, which would otherwise rise to destructive levels due to the tube's...

ed compact fluorescent bulbs (such as the common PL-13) use a large wedge-like base, they are designated as bi-pin or quad-pin bases.

Christmas mini lights

Billions of wedge-base bulbs are used in miniature (T1¾ or 5mm) Christmas lights, where they are easy and therefore inexpensive to manufacture and assemble into their sockets. However, each manufacturer has a slightly different type of wedge base differing in exact dimensions (or even hexagonal instead of round), so the plastic bases often need to be swapped when replacing bulbs. (The wedge bases are now usually not even supplied with the bulbs, which cost nearly as much as buying a new set, typically 10 bulbs for a dollar but a new set of 100 for two dollars.)

Modern sets typically have a long and thin wedge that extends all the way down to the back end of the socket, separating the two electrical conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...

s and contacts and preventing water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 between them when used outdoors. Many sets have an optional "locking" tab on the edge of the base that snaps onto or into the side of the socket, to prevent bulbs from becoming loose and falling out and causing the set to fail to light. This is problematic for light sets with cover
Christmas ornament
Christmas ornaments are decorations that are used to festoon a Christmas tree.Ornaments take many different forms, from a simple round ball to highly artistic designs...

s like icicle
An icicle is a spike of ice formed when water dripping or falling from an object freezes. Typically, icicles will form when ice or snow is melted by either sunlight or some other heat source , and the resulting melted water runs off into an area where the ambient temperature is below the freezing...

s, which will not fit over this type of base or socket unless they have a special notch, which can in turn allow rainwater or snowmelt into the decoration
Christmas decoration
A Christmas decoration is any of several types of decorations used at Christmastime. The traditional colours of Christmas are pine green , snow white, and heart red. Blue and white are often used to represent winter, or sometimes Hanukkah, which occurs around the same time. Gold and silver are...


Special twinkle bulbs often have special bases which they are permanently glued into, to keep the user from putting too many in a strand, or into strands not designed for them. General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...

 produced sets in the late 1970s
File:1970s decade montage.png|From left, clockwise: US President Richard Nixon doing the V for Victory sign after his resignation from office after the Watergate scandal in 1974; Refugees aboard a US naval boat after the Fall of Saigon, leading to the end of the Vietnam War in 1975; The 1973 oil...

 or early 1980s
File:1980s decade montage.png|thumb|400px|From left, clockwise: The first Space Shuttle, Columbia, lifted off in 1981; American President Ronald Reagan and Soviet leader Mikhail Gorbachev eased tensions between the two superpowers, leading to the end of the Cold War; The Fall of the Berlin Wall in...

 with special green-tipped clear "fuse
Fuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...

" bulbs that had special bases at both ends of a set. Modern sets also often have larger sockets at each end of each circuit
Electrical network
An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources and switches. An electrical circuit is a special type of network, one that has a closed loop giving a return path for the current...

 (i.e. two circuits of 50 in a typical 100 incandescent set) because of the third wire, and therefore a different wedge base with a wider separator that cannot be inserted into other regular sockets.

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 sets also have special bases that enforce electrical polarity
Electrical polarity
Electrical polarity is present in every electrical circuit. Electrons flow from the negative pole to the positive pole. In a direct current circuit, one pole is always negative, the other pole is always positive and the electrons flow in one direction only...

, and keep them from being used in incandescent sets. Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....

-branded sets and most store brand
Store brand
Store brands are a line of products sold by a retailer under a single marketing identity. They bear a similarity to the concept of House brands, Private label brands in the United States, own brands in the UK, and home brands in Australia and generic brands...

s use an offset
The term offset may refer to:* Carbon offset, a financial instrument aimed at a reduction in greenhouse gas emissions* Offset agreement, trade practice in Aerospace and Defense Industry...

, with the longer anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....

 (positive lead) being lower and the shorter cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...

 (negative lead) being higher on the wedge base. GE-branded sets (no longer actually made by GE) use a larger round base with a tab that sticks out to one side. A small resistor
A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...

may also be contained in the base of older two-volt LED colors (red, orange, yellow) when in a mixed-color set, so that they match the three volts needed by the newer colors (blue, deep green, purple, white), however other manufacturers only change the value of the resistor that is a part of the cord set itself.
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