The Ford F-600 Super Duty uses a 12961 bulb size for the front side marker and a 3157 bulb size for the rear side marker. The replacement chart covers 2021 to 2022 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 Ford F-600 Super Duty uses two distinct bulb types across its side marker positions for the 2021-2022 model years: the 12961 at the front and the 3157 at the rear.
The 12961 is a Philips part number designation for a miniature wedge bulb in the T10 form factor, fitted with a W2.1x9.5d base, rated at 12V and 5W.
The T10 form factor is a small tubular bulb type widely used in low-intensity automotive lighting positions, consistent with the modest 5W power rating of the 12961.
The W2.1x9.5d base designation refers to a wedge-style base with a 2.1mm wire width and a 9.5mm insertion depth, which determines physical socket compatibility.
The 3157 is an ANSI standard bulb recognized across the United States and Canada, meaning its specifications are standardized rather than proprietary to a single manufacturer.
The 3157 is a dual-filament wedge bulb in the T25 form factor, operating at 12V with a 27W high filament and a 7W low filament, which allows it to serve two brightness levels within a single housing.
The dual-filament design of the 3157 is a common characteristic in rear lighting positions, where a single bulb may need to function at different intensities depending on the lighting mode active at a given moment.
The front and rear side marker positions on the Ford F-600 Super Duty are not interchangeable, as the 12961 and 3157 differ in base type, form factor, wattage, and filament count.