International R121 front side marker bulbs measure 194 in size, while rear side marker bulbs measure 97, with each bulb type specified for its corresponding location. The replacement chart covers 1953 to 1955 production years and details bulb size specifications across the vehicle range.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The International R121 uses two distinct bulb types across its side marker positions: the 194 at the front and the 97 at the rear, both conforming to ANSI standards recognized in the United States and Canada.
Both bulb types are specified uniformly across the 1953-1955 model years for Light Duty variants of the International R121.
The 194 is a T10 miniature wedge bulb, meaning it uses a wedge-style base rather than a metal socket pin, which is a common trait of smaller indicator and marker lamps in mid-century vehicles.
The 194 operates at 12 volts with a power draw of 3.78 watts, placing it among the lower-wattage bulbs used in automotive marker applications.
The 97 uses a BA15s single-contact bayonet base, a base type that locks into its socket with a twist-and-push motion and features a single contact point at the base.
The 97 is rated at 12 volts and 13 watts, a significantly higher wattage than the 194, reflecting its role in the more visible rear side marker position.
The 97 is described as a variant of the 1156 bulb type. Despite this relationship, the two are not directly interchangeable, as physical and electrical differences exist between variants within the same family.
The T10 wedge form factor of the 194 and the BA15s bayonet base of the 97 are mechanically incompatible with each other, making front and rear side marker sockets non-interchangeable on the International R121.