Diamond Reo C120 high beam headlight bulbs use H5001 size while low beam headlight bulbs use H6005 size. Replacement bulb specifications in the chart cover 1992 to 1998 vehicle production years.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Diamond Reo C120 uses the H5001 for high beam and the H5006 for low beam across the 1992-1993 and 1997-1998 model years covered in these specifications.
Both the H5001 and H5006 are sealed beam units, meaning the lens, reflector, and filament are fused into a single glass assembly. When the filament fails, the entire unit is replaced rather than an internal bulb.
The H5001 is a 4-inch square sealed beam unit operating at 12 volts and conforming to ANSI standards recognized in both 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 applicable in the United States and Canada.
The square profile of the H5001 and the round profile of the H5006 make the two units physically incompatible with each other, so the high beam and low beam housings on the C120 are not interchangeable.
The ANSI designation on both units indicates standardized photometric and dimensional requirements, which means compliant replacements from different manufacturers are generally interchangeable at the unit level provided the correct type code is matched.