Citroen D21 headlight bulbs utilize H5001 size for high beam and H5006 size for low beam applications. The replacement chart covers 1969 through 1972 production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Citroen D21 uses two sealed beam types across its 1969-1972 model years: H5001 for high beam and H5006 for low beam headlights.
Both the H5001 and H5006 are sealed beam units, meaning the lens, reflector, and filament are fused into a single assembly. When the filament fails, the entire unit requires replacement rather than just the bulb.
The H5001 is a 4-inch square sealed beam unit operating at 12 volts, conforming to ANSI standards applicable in the United States and Canada.
The H5006 is a 5.75-inch round sealed beam unit, also rated at 12 volts and built to the same ANSI standard as the H5001.
The square form factor of the H5001 and the round form factor of the H5006 make the two units physically incompatible with each other's housings, as each is designed for a distinct mounting configuration.
ANSI standardization of both units means that any manufacturer producing H5001 or H5006 sealed beams to that specification produces a dimensionally and electrically equivalent unit.