Bi-pin lamp base

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A metal halide lamp with a bipin cap

A bipin or bi-pin, (sometimes referred to as two-pin, bipin cap or bipin socket), is a type of lamp fitting. They are included in the IEC standard "IEC 60061 Lamp caps and holders together with gauges for the control of interchangeability and safety". They are used on many small incandescent light bulbs (especially halogen lamps), and for starters on some types of fluorescent lights as well.

Some lamps have pins placed closer together, preventing them from being interchanged with bulbs that are too high power, which may cause excessive heat and possibly fire. These are sometimes called "mini-bipin". Where the terminals of the lamp are bent back onto the sides of the base of the bulb, this forms a wedge base, often used in small bulbs for automotive lighting.

The bi-pin base was invented by Reginald Fessenden for the 1893 World's Fair in Chicago. After Westinghouse won the contract to wire and illuminate the first electrified fair with AC instead of archrival Thomas Edison's DC, Edison and his General Electric company refused to allow his patented Edison screw-base bulbs to be used. Westinghouse overcame this by inventing the bi-pin base for use at the fair.[1]


Type Image IEC 60061-1 Standard Sheet Pin centre to centre Pin diameter Usage
G4 G4 bi-pin connector 7004-72-3 4.0 mm 0.65-0.75 mm small halogens of 5/10/20 watt and 6/12 volt
GU4 7004-108-2 4.0 mm 0.95-1.05 mm mr11 & mr8
GY4 7004-72A-1 4.0 mm 0.65-0.75 mm
GZ4 7004-67-3 4.0 mm 0.95-1.05 mm mr11 & mr8
G5 7004-52-7 5 mm T4 and T5 fluorescent tubes
G5.3 G5.3 bi-pin connector 7004-73-2 5.33 mm 1.47-1.65 mm
G5.3-4.8 7004-126-1
GU5.3 7004-109-2 5.33 mm 1.45-1.6 mm
GX5.3 7004-73A-2 5.33 mm 1.45-1.6 mm (ROUND PINS) MR16 and other small halogens of 20/35/50 watt and 12/24 volt
GY5.3 7004-73B-2 5.33 mm (FLAT PINS)
G6.35 7004-59-6 6.35 mm 0.95-1.05 mm
GX6.35 7004-59-6 6.35 mm 0.95-1.05 mm
GY6.35 7004-59-6 6.35 mm 1.2-1.3 mm Halogen various wattage (e.g. 50 W/100 W), various voltage (e.g. 12/24 V), Common for task lighting, landscape lighting
GZ6.35 7004-59A-3 6.35 mm 0.95-1.05 mm
G8 N/A 8.0 mm Halogen 35-100 W 120 V
GY8.6 N/A 8.6 mm Halogen up to 100 W, 120 V
G9 G9 bi-pin connector 7004-129-3 9.0 mm Halogen 120 V (US) / 230 V (EU), also used for LED lamps.
G9.5 7004-70-2 9.5 mm 3.10-3.25 mm Common for theatre use, several variants
GU10 7004-121-2 10 mm Twist-lock 120/230-volt MR16 halogen lighting of 35/50 watt, since the mid-2000s. Also used for compact fluorescents or LED lamps.
GZ10 7004-120-1 10 mm Twist-lock 120/230-volt MR16 halogen lighting of 35/50 watt, differs from GU10 by use of a dichroic reflector. GZ10 fixtures can also use GU10 bulbs, but not vice versa.
G12 7004-63-2 12.0 mm 2.35 mm Used in theatre and single-end metal halide lamps
G13 7004-51-10 0.50 in (12.7 mm) 0.093 in (2.35 mm) common T8, T10 and T12 fluorescent tubes
G23 7004-69-1 23 mm 2 mm
GU24 7004-78-5 24 mm Twist-lock for self-ballasted compact fluorescents, since the 2000s
G38 7004-76-1 38 mm 11.1 mm Mostly used for high-wattage theatre lamps
GX53 7004-142-2 53 mm Twist-lock for puck-shaped under-cabinet compact fluorescents and LED lamps, since the 2000s
GX70 N/A 70 mm Twist-lock for puck-shaped compact fluorescents or LED lamps

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 two diameters, being larger near the ends, in order to twist-lock into position in the socket (the transition between the two diameters is a right-angle step rather than a taper); in others, the base of the lamp has a groove which can be held by a spring or clip.[2]

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 tubes (both halogen and fluorescent) with one pin at each end, as well as high-output fluorescents with recessed or shrouded contacts, which are not covered here.

See also[edit]


  1. ^ *U.S. Patent 543,280, incandescent electric lamp
  2. ^ "index". 2012-03-09. Archived from the original on April 29, 2011. Retrieved 2012-04-25.

External links[edit]