HID bulb size for stock headlights?

[RedRide]

Allow me to clarify this a bit.....

H-4 and 9003 are actually the same bulb in the sense that they are physically interchangeable.

Originally, there was just the H-4 which was used mainly in European cars.

However, when US manufacturers wanted to use the H-4 bulb, it did not meet US standards because the manufacturing specs of the light beam aming portion of the bulb was not tight enough.

So, a new, tighter manufacturing spec was created and the bulb was named "9003"

However a qualty H-4 bulb such as PIAA have their own tighter specs and its beam aiming is just as good as a 9003.

So, the Yaris will accept either a 9003 or a quality H-4 bulb.
I would just stay away from "bargin" H-4 bulbs as you don't know what you are getting.

Personally, I'm currently using "PIAA Xtreme White Plus" H-4 and the aiming is spot on.