What Is a GU10 Bulb?

Bayonet mount refers to a fastening mechanism that consists of slots and pins that interlock. GU10 is a type of bayonet mount used for certain kinds of light bulbs.

GU10 Mount Coupling

GU10 bulbs attach to a two-pin bayonet mount.

GU10 bayonet mounts contain a male side with one or multiple pins, and a female side with matching slots. Springs holds the pins in position. To disconnect the mount, the two parts must be pushed together to overcome the spring mechanism.

Bulb Caps

Bulbs used in bayonet mounts contain two or three pins on opposite sides of the cap, or bayonet mount. A bipin, also known as a two-pin or bipin cap, refers to a standard for lamp fittings from the International Electrotechnical Commission (IEC).


Bayonet caps are coded by type. Type G caps refers to bipin caps. GU indicates the bipin cap includes a mechanism to support the light fixture. Some GU caps possess pins that are larger at the ends in order to twist-lock the socket into position. The number in the code refers to the diameter of the base. For example, a GU10 has a 10 mm (millimeter) base cap.