The suffix after the G indicates the pin spread; the G dates to the use of Glass for the original bulbs. GU usually also indicates that the lamp provides a mechanism for physical support by the
luminaire: in some cases, each pin has a short section of larger diameter at the end (sometimes described as a "peg" rather than a "pin"); the socket allows the bulb to lock into place by
twisting it; in others, the base of the lamp has a groove which can be held by a spring or clip. A
lowercase "q" at the end of the designation indicates that it is a quad-pin base, with two bi-pin pairs. These are used with
compact fluorescent tubes that plug into a
light fixture that has a permanent ballast. There are also double-ended halogen and fluorescent tubes with one pin at each end, and high-output fluorescents with recessed or shrouded contacts, which are not covered here. File:Lampg4.jpg|Halogen lamps with GU4 (left) and G4 (right) bases File:Lamp6-35.jpg|Halogen lamp with G6.35 base File:Halogenmetalldampflampe.jpg|
Metal halide lamp with G8.5 base File:Lampg9.jpg|Halogen lamp with G9 looped-pin base File:Lampgu10.jpg|Halogen lamp with GU10 twist-lock base ==See also==