A-series light bulb Wikipedia
The A-series light bulb is the "classic" type of light bulb that has been the most commonly used type for general-purpose lighting applications since the early 20th century. It has a pear-like shape and an Edison screw base. The number that follows the "A" within the A series indicates the width of the bulb in one-eighth inch units .
The most commonly used A-series light bulb type is the A19 bulb (or its metric equivalent, the A60 bulb), which is 2 3⁄8 inches (60 mm) wide at its widest point and approximately 4 3⁄8 inches (110 mm) in length, and has a one-inch long (type E26, i.e. 26 millimeters in diameter) Edison screw base. Other base types most commonly used in UK, Australia, and New Zealand include the E27 (i.e. 27 millimeters in diameter) Edison screw base (which also fit E26 sockets), and less commonly these days; the B22 Bayonet twist type base.United States - E26 Edison Screw
Canada - E26 Edison Screw
Japan & Taiwan - E26 Edison Screw
Australia - E27 Edison Screw (or B22 Bayonet Cap)
Europe - E27 Edison Screw
United Kingdom - E27 Edison Screw (or B22 Bayonet Cap)
Although most A-series bulbs have historically used incandescent lighting technology, some other technologies – such as Compact Fluorescent (CFL) or LED lamps – have been used in A-series bulbs more recently.