GMC Astro high beam headlight bulbs use H5001 size while low beam headlight bulbs use H5006 size. The replacement chart covers 1984 to 1988 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 Astro Tiltmaster uses the H5001 for high beam headlights across all listed model years, 1984-1988. This unit conforms to the ANSI standard recognized in both the United States and Canada.
The H5001 is a 4-inch square sealed beam unit operating at 12V. Sealed beam construction means the lens, reflector, and filament are fused into a single housing, so the entire unit is replaced rather than an internal bulb.
Low beam headlights on the Tiltmaster across the same 1984-1988 span use the H5006, also an ANSI-standardized sealed beam unit rated at 12V.
The H5006 is a 5.75-inch round sealed beam unit. Like the H5001, it is not serviceable at the bulb level; the complete assembly is the replaceable component.
The H5001 and H5006 are physically distinct units. The H5001 is square and smaller, while the H5006 is round and larger, making the two non-interchangeable between high and low beam positions.
Both the H5001 and H5006 share the same 12V operating voltage and the same ANSI certification scope, covering the US and Canadian markets.