The Mack Granite (GU) front turn signal bulb uses 3457NA or 1157 size, while the rear turn signal bulb uses 1157 size. The replacement chart covers 2011 through 2022 vehicle 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 Mack Granite (GU) front turn signal specification splits into two fitments depending on headlamp type: the 3457NA applies to trucks equipped with halogen capsule headlamps, while the 1157 applies to those equipped with sealed beam headlamps. This distinction holds across the full 2011-2022 model range covered by the specifications.
The 3457NA is a dual-filament T25 wedge bulb rated at 12V with a 27W high filament and a 7W low filament. Its natural amber glass produces a yellow-tinted output without relying on a colored lens or coating to achieve the amber signal color.
The 1157 is a dual-filament bulb fitted with a BAY15d bayonet base, rated at 12V with a 21W high filament and a 5W low filament. The BAY15d base uses two offset pins to prevent incorrect insertion, a design that distinguishes it from the single-contact 1156 base.
Both the 3457NA and 1157 carry ANSI standardization recognized in the United States and Canada, meaning their physical and electrical characteristics conform to a defined industry specification rather than being proprietary to a single manufacturer.
The rear turn signal position on the Granite (GU) uses the 1157 exclusively across all model years from 2011-2022, with no headlamp-type condition applied. This makes the rear fitment unconditional, unlike the front.
The 3457NA and 1157 are not interchangeable. The 3457NA uses a wedge base, while the 1157 uses a BAY15d bayonet base. These two base types are physically incompatible with each other's sockets.
Although both bulbs are dual-filament designs operating at 12V, their wattage ratings differ. The 3457NA draws more power on its high filament (27W versus 21W) and more on its low filament (7W versus 5W) compared to the 1157.
The dual-filament construction in both bulb types serves a functional purpose in automotive turn signal circuits: one filament typically handles the turn or brake signal function at higher intensity, while the second filament handles a lower-intensity running or parking light function.