The bureaucrats in Washington insisted on assigning it a different number so that it didn't look like they were giving in to reason or common sense when they finally began allowing it on USA market cars (with an unfortunately altered beam pattern) about a decade ago.

One good thing is that the Type A, the H-4/9003, and the traditional USA sealed beams with dual filaments (high and low beam in one reflector lens unit) all take the same connector, whereas 9004 and 9007 bulbs require a different wiring pigtail with a badly designed connector to hook up to the car's wiring. If it should happen that you need to replace some Type A bulbs before you have time to do any conversion, try motorcycle shops. Perhaps also some of our European net readers can inform us as to whether conversion kits from Type-A to H-4 might still be on the market over there.