Mack Granite (GU) Tail Light Bulb Size

The Mack Granite (GU) tail light bulb size is 1157, a specification documented for this heavy-duty truck model. The replacement chart covers vehicle production data spanning 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	US Type	EU Type	Shop
2011-2022	1157	P21/5W	Check Price

Bulb Specifications

Description	Type	Shop
ANSI standard (US & Canada). Dual-filament bulb with BAY15d bayonet base. 12V, 21W/5W.	1157	Check Price
ECE standard (Europe & worldwide). Dual-filament signalling bulb with BAY15d bayonet base. 12V, 21W/5W.	P21/5W	Check Price

Other Locations

Additional Notes

The Mack Granite (GU) uses the 1157 bulb for the tail light position across the 2011-2022 model years.
The 1157 is an ANSI-standardized bulb type, meaning its physical and electrical specifications are governed by a recognized North American standard used in both the United States and Canada.
The 1157 is a dual-filament bulb, which allows it to serve two lighting functions within a single housing, typically combining a lower-intensity running light with a higher-intensity brake or stop light signal.
The bulb operates on a 12-volt electrical system and carries a wattage rating of 21W on the high-intensity filament and 5W on the low-intensity filament.
The 1157 uses a BAY15d bayonet base, a two-pin base type where the two pins are offset at different heights to prevent incorrect installation orientation.
The BAY15d base is a keyed fitment, meaning a single-filament bulb with a standard BAY15s base is not a compatible substitute, as the pin configuration differs.