When it comes to light bulb choice, and the matching lamp or fixtures socket, there are a number of different base type and sizes to choose from. Here are some of the caps and bases your are most likely to encounter.

Incandescents

References
Cap Diameter
Description
Image
BC/B22/B22d/Ba22d 22mm Bayonet Cap Bayonet Cap
SBC/B15/B15d/Ba15d 15mm Small Bayonet Cap Small Bayonet Cap
SES/E14 14mm Small Edison Screw Small Edison Screw
ES/E27 27mm Edison Screw Cap Edison Screw Cap
CES/E12 12mm Candelabra Edison Screw Candelabra Edison Screw

 

Halogens & LEDs

References
Pin Spacing
Image
GU4/MR11 4mm GU4/MR11
GU5.3/MR16 5.3mm GU5.3/MR16
GU10 10mm GU10
G4 4mm G4
GT6.35 6.35mm GT6.35
G9 9mm G9
R7/R7s/RX7s 7mm R7/R7s/RX7s

 

Fluorescents

Reference
Pin Spacing
Tube Type
Tube Diameter
Image
T4/G5 5mm Straight 12mm T4/G5
T5/G5 5mm Straight 15mm T5/G5
T8/G13 13mm Straight 25mm T8/G13
T9/G10q N/A Circular 29mm T9/G10q
T12/G13 13mm Straight 38mm T12/G13
GR10q N/A 2D Compact Fluorescent N/A GR10q