The GMC PM251 uses H6024 bulb size for both high beam and low beam headlight applications. The replacement chart covers 1956 to 1957 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 H6024 is a 7-inch round sealed beam unit operating at 12 volts, conforming to ANSI standards recognized in both the United States and Canada.
Unlike bulb-and-housing systems, the H6024 is a sealed beam unit, meaning the lens, reflector, and filament are fused into a single assembly that is replaced as a whole when the light fails.
The GMC PM251 uses the H6024 for both the high beam and low beam headlight positions across the 1956-1957 model years, making it the sole headlight bulb type in these specifications.
Because the high beam and low beam positions share the same H6024 specification, the PM251 used a dual-filament sealed beam arrangement rather than separate single-filament units for each function.