Some people asked me what is the difference between h7 and h11. Ok, look carefully.
H1: single filament and single holder, high beam light
H3: used more often on Japan branded cars
H4: double filament and three holders, both low and high beam light are in one bulb
H7: single filament and double holders, low beam light
(sometimes, h1 and h7 are also used for fog light )
H11: used for fog light
For more halogen light information, you can refer to: http://www.sourcingmap.com/car_light.php