International A100 Truck front and rear turn signal bulbs both utilize a 198 size bulb for optimal lighting performance. The replacement chart covers 1957 to 1958 production specifications for turn signal bulb applications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The International A100 Truck uses the 198 bulb for both front and rear turn signal positions across the 1957-1958 model years.
The 198 is an ANSI-standardized bulb type, meaning its specifications conform to a defined North American standard recognized in both the United States and Canada.
The 198 bulb follows a T5 miniature wedge form factor. The T5 designation refers to a tubular envelope with a width of 5/8 inch, and the wedge base type means the glass envelope itself acts as the base, with no separate metal shell or pins.
At 12 volts and 2 watts, the 198 is a very low-output bulb, consistent with indicator rather than illumination applications.
The uniform use of the 198 bulb across all four turn signal positions on the International A100 Truck means a single bulb type serves the entire turn signal circuit on the vehicle.
The Light Duty classification noted in the specifications refers to the vehicle trim or configuration level, not a rating of the bulb itself.
Because the 198 uses a wedge base, it is not interchangeable with bayonet-base or screw-base bulbs of similar wattage, even if the voltage and wattage ratings match.