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Standard fittings
Most domestic and industrial light bulbs have a metal fitting (lamp base) compatible with standard sockets. General Electric introduced standard fitting sizes for tungsten incandescent lamps under the Mazda trademark in 1909. This standard was soon adopted across the United States, and the Mazda name was used by many manufacturers under license through 1945.
Screw thread
In each designation, the E stands for Edison, who created the screw-base lamp, and the number is the diameter of the screw base in millimeters. (This is even true in North America, where designations for the actual bulb glass diameter are in eighths of an inch.)
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N. America
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Europe
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E5
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Miniature: (Rare) Generally used only for low-voltage applications such as with a battery. Some large flashlights use the E5 bulb.
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E12
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E10 & E11
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Candelabra: Commonly used in candelabras and other decorative lighting. The bulb is usually flame shaped, but small bulbs and globes also use the E12.
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E17
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E14
(Small ES)
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Intermediate: Large outdoor Christmas lights use an intermediate base, as do some desk lamps and many microwave ovens. Formerly Emergency exit signs also tended to use the intermediate base (but modern exit signs must use LEDs).
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E26
(MES)
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E27
(ES)
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Medium or standard: The standard light bulb base used in the majority of household bulb applications. A medium screw base should not carry more than 25 amperes current; this may limit the practical rating of low-voltage lamps. There is also a rare "admedium" size (E29), incompatible with standard and used to frustrate thieves of bulbs used in public places.
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E39
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E40
(GoliathES)
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Mogul: The largest size E39 is now only used in large street lights, although a few high-wattage household lamps (such as a 100/200/300-watt three-way) use it as do 300, 500, 750, 1000 and 1500 watt light bulbs.
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Pin Bases
In the chart below, the suffix after the G indicates the pin size. GU indicates that each pin has two diameters, being larger near the ends, in order to twist-lock into position in the socket. The transition between the two diameters is a right-angle step rather than a taper. There are also double-ended bipin tubes with one pin at each end.
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Type
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Pin Centering
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Pin Dimension
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Eco-$mart Product
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G4
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4.0 mm
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0.65-0.75 mm
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GU4
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4.0 mm
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0.95-1.05 mm
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GY4
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4.0 mm
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0.65-0.75 mm
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GZ4
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4.0 mm
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0.95-1.05 mm
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G5
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5 mm
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G5.3
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5.33 mm
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1.47-1.65 mm
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GU5.3
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5.33 mm
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1.45-1.6 mm
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GX5.3
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5.33 mm
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1.45-1.6 mm
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G6.35
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6.35 mm
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0.95-1.05 mm
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G6.35
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6.35 mm
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0.95-1.05 mm
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GY6.35
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6.35 mm
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1.2-1.3 mm
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GZ6.35
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6.35 mm
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0.95-1.05 mm
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G9
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9.0 mm
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GU10
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10 mm
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G13
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12.7 mm (½ in.)
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Reference: International Electrotechnical Commission
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