Some of the most common light bulb bases are: E27, E14, E12, B22, B15, Pin-Based (Bi-Pin), G4, GU10 (twist and lock base with two pins), G9, R7S (linear base used in halogen bulbs), MR16 (reflector bulb with a bi-pin base) and PAR(parabolic aluminised reflector bulb with a variety of bases).