page_title: Edison screw
section_title: Types
hierarchical_section_title: Edison screw / Types
caption_attribution_description: English: A standard US three way light bulb socket.
context_page_description: Edison screw is a standard lightbulb socket for electric light bulbs. It was developed by Thomas Edison, patented in 1890, and was licensed in 1909 under General Electric's Mazda trademark. The bulbs have right-hand threaded metal bases which screw into matching threaded sockets. For bulbs powered by AC current, the thread is generally connected to neutral and the contact on the bottom tip of the base is connected to the "live" phase.
  In North America and continental Europe, Edison screws displaced other socket types for general lighting. In the early days of electrification, Edison screws were the only standard connector, and appliances other than light bulbs were connected to AC power via lamp sockets. Today Edison screw sockets comply with international standards.
context_section_description: Specifications for all lamp mount types are defined in the following American National Standards Institute (ANSI) and International Electrotechnical Commission (IEC) publications:
  Lamp Caps—ANSI C81.61 and IEC 60061-1
  Lamp Holders—NSI C81.62 and IEC 60061-2
  Gauges (to ensure interchangeability)—ANSI C81.63 and IEC 60061-3
  Guidelines for Electrical Lamp Bases, Lampholders and Gauges—ANSI C81.64 and IEC 60061-4
  Generally, the two standards are harmonized, although several types of screw mount are still defined in only one standard.
  In the designation "Exx", "E" stands for "Edison" and "xx" indicates the diameter in millimeters as measured across the peaks of the thread on the base (male), e.g., E12 has a diameter of 12 mm.  This is distinct from the glass envelope (bulb)  diameter, which in the U.S. is given in eighths of an inch, e.g., A19, MR16, T12.
  There are four commonly used thread size groups for mains supply lamps:
  Candelabra: E12 North America, E11 in Europe
  Intermediate: E17 North America, E14 (Small ES, SES) in Europe
  Medium or standard: E26 (MES) in North America, E27 (ES) in Europe
  Mogul: E39 North America, E40 (Goliath ES) in Europe.
  The E26 and E27 are usually interchangeable, as are the E39 and E40, because there is only a 1 mm difference in thread outside diameter. E11 and E12 are not interchangeable. Other semi-standard screw thread sizes are available for certain specific applications.
  The large E39 "Mogul" and E40 "Goliath" base are used on street lights, and high-wattage lamps (such as a 100 W / 200 W / 300 W 3-way) and many high-intensity discharge lamps. In areas following the U.S. National Electrical Code, general-use lamps over 300 W cannot use an E26 base and must instead use the E39 base. Medium Edison screw (MES) bulbs for 12 V are also produced for recreational vehicles. Large outdoor Christmas lights use Intermediate base, as do some desk lamps and many microwave ovens. Previously, emergency exit signs also tended to use the intermediate base, but U.S. and Canadian rules now require long-life and energy-efficient LED lamps, which can be purchased inside a conventional Edison base bulb as a retrofit. A medium screw base should not carry more than 25 amperes current; this may limit the practical rating of low voltage lamps.
  E29 "Admedium" bases are used for special applications, for example UV spotlight lamps in magnetic crack detection machines.
  In countries that use 220–240 Volt AC domestic power, standard-size E27 and small E14 are the most common screw-mount sizes and are prevalent throughout continental Europe and China.
  In 120-Volt North America, 100-Volt Japan and 110-Volt Taiwan, the standard size for general-purpose lamps is E26.
  E12 is typically used for candelabra fixtures. E17 is also sometimes used, especially in small table lamps and novelty lighting, and occasionally the lights on newer ceiling fans. Christmas lights use various base sizes E17 for C9 bulbs, E12 for C7 bulbs, E10 for decades-old series-wired C6 bulb sets in the U.S., and an entirely different wedge base for T1¾ mini lights. For a short time early on, these mini lights were manufactured using E5 screw bases.
  A tiny E5 or E5.5 size is used only for extra-low voltages, such as in interior illumination for model buildings, and model vehicles such as model trains. These are often called "pea bulbs" if they are globe-shaped, but they commonly look like mini Christmas bulbs, or large "grain-of-wheat" bulbs. E10 bulbs are common on battery-powered flashlights, as are bayonet mounts (although those are usually held in with a circular flange located where the base meets the glass envelope of the bulb). The E11 base is sometimes used for 50/75/100-watt halogen lights in North America, where it is called the "mini-can", and tighter threads are used to keep them out of E12-base nightlights and other places where they could start a fire.
  There are also adapters between screw sizes, and for adapting to or from bayonet caps. A socket extender makes the bulb stick out further, such as to accommodate a compact fluorescent lamp that 
caption: Three-way E26d light socket
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