International WorkStar 7600 front and rear turn signal bulbs utilize 3157NA and 3157 sizes respectively. The replacement chart covers 2008 through 2017 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 7600 uses the 3157NA bulb for the front turn signal across all specified model years, spanning 2008-2017, with no variation in that position throughout the listed range.
The 3157NA is a dual-filament T25 wedge bulb rated at 12V with a 27W high filament and a 7W low filament, conforming to ANSI standards applicable in the United States and Canada.
The "NA" suffix in the 3157NA designation indicates natural amber glass, meaning the bulb produces an amber-colored output without relying on a colored lens or housing to achieve that effect.
The rear turn signal on the WorkStar 7600 uses the 3157 bulb across all specified model years from 2008-2017, sharing the same T25 form factor, 12V operating voltage, and 27W/7W dual-filament configuration as the 3157NA.
The sole technical distinction between the 3157NA and the 3157 is the glass envelope: the 3157NA has natural amber glass, while the 3157 has a clear glass envelope, making the two bulbs non-identical despite their otherwise matching electrical and physical specifications.
Because the 3157 and 3157NA share the same T25 wedge base and electrical ratings, they are physically interchangeable, but substituting a clear 3157 in place of a 3157NA front position may alter the color output if the housing itself is not amber-tinted.
The dual-filament design of both bulb types allows a single bulb to serve two lighting functions, with the 27W filament typically handling the brighter turn signal flash and the 7W filament serving a secondary role such as a parking or running light.
Both the 3157 and 3157NA operate on a 12V electrical system, which is consistent with standard automotive and commercial truck low-voltage architecture.