The screw is the part of the bulb that attaches to the lamp holder. It’s usually made of metal, amongst other materials, which allows electricity to pass through and illuminate the bulb once it’s in place.
The nomenclature used in (bulb) screws is the following::
Types of Lamp holder
Edison type screw
B o BA
Swan or Bayonet type holder.
Pressure contact for circular tubes
Contact by simple pressure clamps
Contact by reinforced pressure clamps
Contact by clamps for bulbs with protection from rear heat emission
Contact by clamps for bulbs with high level of rear heat emission
Screws for rectilinear lamps with simple terminals
Screws for rectilinear lamps with reinforced terminals
Screws for rectilinear lamps with male terminals
Lamp holder diameters
Low consumption lamps
Bi-Pin type lamps
Small, Edison candle screw
Standard Edison screw
Giant Edison screw
Number/Amount of contacts
Most commonly used/ common screws
E14 Used for bulbs that are small in size, mostly incandescent, like for example; Candle or Drop lamps.
E27 The most extensively used holder in Europe. Used for incandescent bulbs, compact fluorescent bulbs, metal halide bulbs, …
E40 Identical to E14 and E27 holders, but designed to withstand higher levels of electrical output.
B22d Commonly used in incandescent bulbs.
GU10 Halogen / Dichroic lamps, LEDs, etc…
GZ10 Halogen / Dichroic lamps, LEDs, etc…
R7s Used in linear halogen bulbs.
Fa4 Used in linear halogen bulbs.
GU4 Mainly used in halogen bulbs / dichroic halogen bulbs.
GU5.3 Mainly used in halogen bulbs / dichroic halogen bulbs.
G53 Halogen bulbs with a wide, reflectable dish.
G9 Halogen bulbs.
G4 Halogen bulbs.
GY6.35 Halogen bulbs.
G5 Halogen bulbs.
G13 Used in fluorescent tubes.
2GX13 Used in circular fluorescent tubes.
2G13 For double fluorescent tubes.
Fa6 Rarely used. Made for low-pressure, mercury lamps.