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Bulb Bases

If you want to get to first base in the bulb business, you have to get the base to fit into the socket. The Standard "Medium" base is an E26. Except, of course, when it’s an E27. This is what happens when different parts of the world with different standard bases trade with each other. For all intents and purposes, an E26 and E27 are interchangeable.

In the chart below, E stands for Edison and the number is the diameter in millimeters.

Bayonet (push-twist) bases fit into sockets with spring-loaded base plates. Some refer to these bayonet bulbs as B or BA.

Halogen bulbs frequently have bases marked G, GU or GY, followed by a number. The second letter, if present, indicates the thickness of the pins. The number is the center-to-center distance between the pins. The typical landscape bulb in your Malibu light is probably a GU5.3, which has 5.3 millimeters from pin center to pin center.

Fluorescent Bases