Mack Granite (GU) Brake Bulb Size

The Mack Granite (GU) brake bulb uses a 1157 size bulb for replacement applications across the specified model line. The replacement chart covers vehicle production years from 2011 to 2022.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
2011-2022	1157

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. 12V, 21W/5W.	1157

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Additional Notes

The Mack Granite (GU) uses the 1157 bulb for the brake light position across the 2011-2022 model years.
The 1157 is an ANSI-standardized bulb type recognized in both the United States and Canada.
It is a dual-filament bulb, meaning it contains two separate filaments within a single envelope, allowing it to serve two distinct lighting functions at different wattages.
The bulb operates on a 12-volt electrical system, consistent with standard automotive voltage.
Its two filaments are rated at 21 watts and 5 watts, where the higher-wattage filament typically handles the brighter stop light function and the lower-wattage filament handles a secondary function such as a tail or running light.
The 1157 uses a BAY15d bayonet base, which is an offset twin-pin base design that prevents incorrect insertion by ensuring the two pins are positioned at different heights.
The BAY15d base is a keyed fitment, meaning bulbs with a standard single-pin or non-offset twin-pin base are not interchangeable with the 1157 even if they appear physically similar.