Some of the most common light bulb bases are: E27, E14, E12, B22, B15, Pin-Based (Bi-Pin), G4, GU10 (twist and lock base with two pins), G9, R7S (linear base used in halogen bulbs), MR16 (reflector bulb with a bi-pin base) and PAR(parabolic aluminised reflector bulb with a variety of bases).

An A15 bulb is pear shaped and is commonly used in appliances and ceiling fans. It has a diameter of 15/8 inches (48 mm) at its widest point. A15 bulbs typically have an E26 base, which is a standard screw base used in the United States.

E26 is the base shape while A15 is the bulb shape.

An A15 bulb has a diameter of 15/8 inches (48 mm) at its widest point.