The International A122 uses a 198 bulb size for both front and rear turn signal applications. The replacement chart covers 1957 to 1958 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 International A122 uses the 198 bulb for both front and rear turn signals across the 1957-1958 model years.
The 198 is an ANSI-standardized bulb type, meaning it conforms to a defined set of electrical and physical characteristics recognized across the United States and Canada.
The 198 bulb follows the T5 miniature wedge form factor, a designation that refers to a tubular glass envelope approximately 5/8 of an inch wide with a wedge-style base that seats directly into a socket without a separate metal cap.
Operating at 12 volts and 2 watts, the 198 is a low-power bulb, consistent with its role in signaling rather than primary illumination.
The wedge base design of the 198 means the bulb is held in place by the socket itself, with the electrical contacts formed by the glass envelope's pinched base rather than by separate metal pins or a bayonet fitting.
The Light Duty classification noted in the International A122 specifications indicates the bulb application is associated with lighter vehicle configurations rather than heavy-duty truck variants.
Because the same 198 bulb size is specified for both the front and rear turn signal positions, a single bulb type serves all four turn signal housings on the vehicle.