The International R121 uses a 198 bulb size for both front and rear turn signal applications. The replacement chart covers vehicle production spanning 1953 to 1955.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 198 bulb is the sole bulb type listed across all turn signal positions for the International R121, appearing in both front and rear applications for the 1953-1955 model years.
The 198 is classified as a miniature wedge bulb, designated T5 in the tubular bulb sizing system, where the number indicates a width of five-eighths of an inch.
The 198 bulb operates at 12 volts and draws 2 watts, placing it among the lower-output bulbs in automotive applications, consistent with its use in signal rather than illumination functions.
The 198 conforms to ANSI standards and carries recognition in both the United States and Canada, meaning it follows a standardized specification shared across North American markets.
The wedge base design of the 198 means the bulb is held in its socket by the tension of the base itself rather than by a separate bayonet or screw mechanism, which is a defining fitment characteristic for replacement purposes.
All entries in the specifications carry a Light Duty designation, which reflects the vehicle's weight class rating rather than a characteristic of the bulb itself.
The 198 bulb size applies uniformly to both the front and rear turn signal positions on the International R121 across the full 1953-1955 span covered in the specifications, indicating no positional variation in bulb type.