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The Edison screw fitting is a system of light bulb connectors, developed by Thomas Edison and...

The Edison screw fitting is a system of light bulb connectors, developed by Thomas Edison and licensed starting in 1909 under the Mazda trademark. The designation Exx refers to the diameter in millimeters. For example, E12 has a diameter of 12 mm. In the United States, the standard size for general purpose lamps is E26. E12 is typically used for candelabra fixtures. E17 is also sometimes used, especially in table lamps. Christmas lights use various base sizes: E17 for C9 bulbs, E12 for C7 bulbs, and E10 for some other types. In countries which use 220–240 volts AC domestic power, E27 and E14 are the most common sizes, although the Bayonet mount is also used. Larger sizes (E39, E40) are used for higher powered lighting, generally for lamps of over 250 watts. Some adapters for wall outlets use an Edison screw. At the turn of the 19th century different lamp manufacturers used different incompatible bases. The Thompson-Houston company used a threaded stud at the bottom of the socket, and a flat contact ring. The Sawyer-Mann or Westinghouse base used a spring clip acting on grooves in the bulb base, and a contact stud at the bottom of the lamp. By about 1908 the Edison base was most