Bi-pin connector

A bipin or bi-pin, (sometimes referred to as two-pin, bipin cap or bipin socket), is a standard from the IEC for lamp fittings. These 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". Some of these, particularly in automotive lighting, have the pins bent back onto the sides of the base of the bulb, this is instead called a wedge base or socket.

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]

Types

Type	Standard	Pin centre to centre	Pin diameter	Usage
G4	IEC 60061-1 (7004-72)	4.0 mm	0.65-0.75 mm	MR11 and other small halogens of 5/10/20 watt and 6/12 volt
GU4	IEC 60061-1 (7004-108)	4.0 mm	0.95-1.05 mm
GY4	IEC 60061-1 (7004-72A)	4.0 mm	0.65-0.75 mm
GZ4	IEC 60061-1 (7004-64)	4.0 mm	0.95-1.05 mm
G5	IEC 60061-1 (7004-52-5)	5 mm		T4 and T5 fluorescent tubes
G5.3	IEC 60061-1 (7004-73)	5.33 mm	1.47-1.65 mm
G5.3-4.8	IEC 60061-1 (7004-126-1)
GU5.3	IEC 60061-1 (7004-109)	5.33 mm	1.45-1.6 mm
GX5.3	IEC 60061-1 (7004-73A)	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	IEC 60061-1 (7004-73B)	5.33 mm	(FLAT PINS)
G6.35	IEC 60061-1 (7004-59)	6.35 mm	0.95-1.05 mm
GX6.35	IEC 60061-1 (7004-59)	6.35 mm	0.95-1.05 mm
GY6.35	IEC 60061-1 (7004-59)	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	IEC 60061-1 (7004-59A)	6.35 mm	0.95-1.05 mm
G8		8.0 mm		Halogen 35-100 W 120 V
GY8.6		8.6 mm		Halogen up to 100 W, 120 V
G9	IEC 60061-1 (7004-129)	9.0 mm		Halogen 120 V (US) / 230 V (EU)
G9.5		9.5 mm	3.10-3.25 mm	Common for theatre use, several variants
GU10		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		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		12.0 mm	2.35 mm	Used in theatre and single-end metal halide lamps
G13		0.50 in (12.7 mm)	0.093 in (2.35 mm)	T8 and T12 fluorescent tubes
G23		23 mm	2 mm
GU24		24 mm		Twist-lock for self-ballasted compact fluorescents, since the 2000s
G38		38 mm	11.1 mm	Mostly used for high-wattage theatre lamps
GX53		53 mm		Twist-lock for puck-shaped under-cabinet compact fluorescents and LED lamps, since the 2000s
GX70		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.