GMC FM350 headlight bulbs utilize H6024 and H6006 sizes for both high and low beam applications. The replacement chart covers 1955 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 GMC FM350 uses two distinct sealed beam unit types across its 1955-1957 model years: the H6024 and the H6006, both operating at 12 volts and conforming to ANSI standards recognized in the United States and Canada.
The H6024 is a 7-inch round sealed beam unit. Because it is a sealed beam design, the entire unit is replaced rather than an internal filament or capsule.
The H6006 follows the same sealed beam construction as the H6024 but is rectangular at 5x7 inches, making the two units physically incompatible with each other despite sharing the same voltage rating.
For the 1956-1957 FM350, both the high beam and low beam headlight positions use the H6024, meaning a single unit type serves both functions across those two years.
The 1955 FM350 uses the H6006 for both the high beam and low beam positions, a different sealed beam format from the one used in subsequent years.
Because the H6024 and H6006 differ in shape and size, they are not interchangeable. Substituting one for the other is not supported by the fitment specifications.