A candelabra base is the name for a small light bulb base that screws into some chandeliers, nightlights, and decorative fixtures. It's the smaller of the two classic old-school Christmas light bulb base sizes. A candelabra base is also called an E12 base.
Candelabra Bulb Base Sizing
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In order for it to be called a candelabra bulb base, it must be the E12 base size. The E in the E12 name stands for Edison, as in an Edison screw-in bulb. Any bulb with the classic screw-in base design has an Edison base. The number 12 stands for the diameter of the base (not the bulb) in millimeters, so an E12 is a screw-in bulb base with a 12-millimeter diameter. The common light bulbs that fit most table and floor lamps have an E26 base, which means the base portion has a 26-millimeter diameter. The E26 is also called a medium or standard base.
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If you have more than one chandelier or fixture in your home that uses bulbs with small bases, it could be confusing when deciding which to buy. Always check the package for the number designations, such as E12 for the candelabra base, to ensure you're buying bulbs that fit a candelabra socket.
By comparison, another common small bulb used in some chandeliers and in appliances has an E17 base, also called an intermediate base. The E17 base is considerably wider and won't fit into a socket made for a candelabra bulb even though the actual bulbs may be of similar height and shape. If you aren't sure of the size of your burned-out bulb and therefore don't know which to buy as replacements, measure the diameter of the base in millimeters.
Bulb Shapes Use Letters Too
When buying bulbs with the candelabra base size, you may notice other letter and number combinations on the package in addition to E12. Manufacturers also use letters to designate specific bulb shapes. For instance, an E12 bulb base often goes along with a C7 bulb, with the C indicating a fairly conical shape, similar to a bulb for a Christmas light strand. A C9 bulb could be of very similar shape, just larger and usually with the E17 base.
A G stands for a globe-shaped bulb, as might be found around some dressing-room mirrors, while a T indicates a tube-shaped bulb with fairly straight sides. An ST stands for straight tapered, indicative of the old-fashioned Edison-style bulbs that look like they're more than a century old. These are common in rustic and vintage industrial-style displays.