A lamp socket, also known as the Edison screw fitting, is a threaded screw base used to hold and connect a light bulb to a power source. Invented by Thomas Edison and marketed in 1909, these sockets typically have right-hand threads, which allow the light bulb to be screwed in clockwise and removed counterclockwise. To deter theft in public places, the threads are sometimes reversed to prevent installation in common light fixtures.
Lamps, light fixtures, and adapters are common types of fixtures that include a lamp socket. Light fixtures as well as lamps incorporate Edison screw lamp sockets into their design not only for holding and energizing the bulb but also to take advantage of the many types of bulbs on the market that use this design. Alternate designs were implemented in the early 1900s that varied from Edison's design but in the end, they fell out of use due to the practicality of the Edison screw.
B Bayonet Collar Base
E Edison Screw Light Base
F Single Pin Type Base
G Multiple Pin Type Light Bulb Base
K Cable Connections
P Pre-focused Light Base
R Recessed Contact(s) Base
S Shell-type Light Bulb Base
T Telephone Slide Base
W Wedge Base
X Special Type Lightbulb Base
Lamp Number of Pin or Contacts
s Single Pin
d Double or Bi-Pin Base Type
t Triple Pin Base or Tri-Pin Base or 3 Pin Base
q Quadruple Pin Base or 4 Pin Base
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