GMC 100 high beam and low beam headlight bulbs utilize H6024, H5001, H6006, and H5006 bulb sizes depending on configuration. The replacement chart covers 1951 through 1959 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 H6006 is the most consistently specified sealed beam unit across the GMC 100's headlight history, appearing in both high beam and low beam positions for the 1951-1955 model years. It is a 5x7-inch rectangular sealed beam unit rated at 12V and conforms to ANSI standards applicable in the US and Canada.
The H6024 is a 7-inch round sealed beam unit operating at 12V under ANSI standards. It serves dual function on the GMC 100, handling both high beam and low beam output within a single unit, and is specified for 1956-1957 as well as for 1958-1959 two-headlamp configurations.
All four bulb types listed across these specifications 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 1958-1959 GMC 100 introduced a four-headlamp configuration as an alternative to the two-headlamp setup, splitting the lighting function between two distinct sealed beam types. The H5001, a 4-inch square unit, handles the high beam role, while the H5006, a 5.75-inch round unit, handles the low beam role in that system.
The two-headlamp and four-headlamp systems on the 1958-1959 GMC 100 are not interchangeable. Each configuration uses a different set of sealed beam units, and the bulb sizes specified for one system are not compatible with the other.
The H5001 and H5006 are exclusive to the four-headlamp variant of the 1958-1959 model years. Neither type appears in any other year within these specifications, making them configuration-specific rather than general-use units across the GMC 100 range.
All sealed beam units listed operate at 12V, which is consistent with the 12-volt electrical systems that became standard in American vehicles during the mid-1950s, replacing earlier 6-volt systems.
The transition from the H6006 rectangular unit to the H6024 round unit between 1955 and 1956 represents a change in sealed beam form factor on the GMC 100, with both types remaining ANSI-standardized and rated at 12V.