Q: What does the screw specification E26, E27, etc, under the product description refer to?
A: The designation for E xx refers to the diameter in millimeters. This includes the U.S, where the bulb glass is listed in eighths of an inch. For example, E12 has a diameter of 12 mm. There are four common sizes of screw-in sockets that are used for line-voltage lamps:

• Candelabra: E12 North America, E11 in Europe
• Intermediate: E17 North America, E14 (Small ES) in Europe
• Medium or standard: E26 (MES) in North America, E27 (ES) in Europe
• Mogul: E39 North America, E40 (Goliath ES) in Europe.

E27 and E14 are the most common sizes in countries that use 220–240 volts AC domestic power. In USA and Japan they use 120- and 100-volt, so the standard size for general-purpose lamps is E26.