International WorkStar 7700 front turn signal bulbs utilize 3157NA size while rear turn signal bulbs use 3157 size. The replacement chart covers 2008 through 2012 production years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The International WorkStar 7700 uses the 3157NA bulb for the front turn signal across the 2008-2012 model years.
The 3157NA is a dual-filament T25 wedge bulb rated at 12V with a 27W high filament and 7W low filament, and it features natural amber-tinted glass.
The natural amber glass of the 3157NA produces an amber signal output directly from the bulb itself, without relying on a colored lens to achieve the required turn signal color.
The rear turn signal on the WorkStar 7700 uses the 3157 bulb across the same 2008-2012 model years.
The 3157 shares the same T25 wedge base, 12V operating voltage, and 27W/7W dual-filament configuration as the 3157NA, differing only in the absence of the natural amber glass coating.
Both the 3157NA and 3157 conform to ANSI standards applicable in the United States and Canada.
Because the 3157 and 3157NA share the same base type and electrical ratings, they are physically interchangeable, though substituting a clear 3157 in place of the 3157NA at the front position may affect the amber color output if the housing lens is also clear.
The dual-filament design of both bulbs allows a single unit to serve two lighting functions, typically combining turn signal operation on the higher 27W filament with a secondary function such as parking or running light on the 7W filament.