Difference between car bulb sizes 9003/HB2/H4?
are these interchangeable ways to call the same bulb size? 9003/HB2/H4
Why is there the same name for the same size bulb?
- 8 years agoFavorite Answer
They are all interchangeable. They all mount the same as far as in a lense and have the same connector. It's just throughout the years manufacturers got more strict on filament placement. Some states have inspection programs that check for DOT bulbs, which usually the H4's aren't. 9003/HB2's are usually the required bulb. The belief was filament location can make the beam pattern shift or change. I think this applies more to fleet vehicles, but if a vehicle manufacture wants to cut corners on part price for a lower assemble cost, they will go for the cheaper part.Source(s): http://candlepowerinc.com/pdfs/H4_9003.pdf