The GMC M300 headlight bulb uses H6024 and H6006 sizes for both high and low beam applications, with the bulb specifications varying across the model line. The replacement chart covers 1954 through 1957 production years and details the corresponding bulb size requirements for each year.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The H6024 and H6006 are the two bulb types specified across all listed model years of the GMC M300, with each type serving both high beam and low beam functions within its respective year range.
Both the H6024 and H6006 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 an internal bulb swap.
The H6024 is a 7-inch round sealed beam unit operating at 12V and conforming to ANSI standards recognized in both the United States and Canada. It is specified for the GMC M300 for the 1956-1957 model years.
The H6006 is a 5x7-inch rectangular sealed beam unit, also rated at 12V and built to the same ANSI standard. It is specified for the 1954-1955 model years.
On the M300, the high beam and low beam positions share the same bulb type within each model year. This indicates a single-unit sealed beam design where one assembly handles both functions, rather than separate dedicated high and low beam housings.
The H6024 and H6006 are not interchangeable with each other. Their physical form factors differ, with the H6024 being round and the H6006 being rectangular, making cross-substitution between the 1954-1955 and 1956-1957 fitments incompatible.