Both G6.35 and GY6.35 are base codes for lamps with bi-pin base connectors, sometimes called miniature bi-pins or mini-bipins. Under the code system set by the International Electrotechnical Commission a G6.35 lamp base has 1.0mm-diameter pins, while a GY6.35 lamp base has 1.25mm-diameter pins.
In lighting systems, a socket is the receptacle that connects to an electrical supply. A base is the part of a lamp or bulb that connects to a socket. There are many types of bases for lamps, including the Edison screw base, the Bayonet mount, the wedge base and pin bases with one, two or four pins.
A lamp base with two metal pins is called a bi-pin base. Bi-pin connectors are very common in bases made for small halogen lamps and linear fluorescent lamps. Under the code system set by the IEC (International Electrotechnical Commission), all bi-pin lamp bases are assigned the prefix G, and a number, which represents the number of millimeters (mm) that separate the two pins.
The space located between two pins on a bi-pin bulb is determined by several factors. Different manufacturers may use different pin spacing, or pins may be deliberately placed closer together to prevent over-lamping. Over-lamping is a situation that occurs when a high-wattage bulb is placed in a socket designed for a lower-wattage bulb, heating up the lamp housing and creating a fire hazard.
In the IEC code system, another letter may follow the G prefix. The second letter represents the configuration of the base, which determines the diameter and shape of the pins. For example, pins may be rounded, square, grooved, fat or slender. Under the IEC code system, G6.35 represents a bi-pin base with a 6.35mm pin spread and 1.0mm-diameter pins. A GY6.35 base code represents a bi-pin base with a 6.35mm pin spread and a 1.25mm-diameter pin.
Lamp bases with a small space between the pins, such as the GY6.35 and G6.35 bases are sometimes called miniature bi-pins or mini-bipins. The GY6.35 and G6.35 bases are typically used for small halogen bulbs.