The Audi RS4 side marker requires a bulb with the unique size 12961 for proper installation. Available data for the specified lighting component covers the period from 2008 through 2008.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Audi RS4 uses the T10 miniature wedge bulb form factor for both its front and rear side markers across the 2007-2008 model years.
The T10 designation refers to a tubular bulb roughly 10mm wide, commonly used in low-intensity automotive lighting positions such as side markers, courtesy lights, and license plate lamps.
The front side marker on the 2007-2008 Audi RS4 takes a 12961, which is a Philips part number for a T10 wedge bulb rated at 12V and 5W with a W2.1x9.5d base.
The rear side marker on the same vehicle takes a 12821, also a Philips part number for a T10 wedge bulb sharing the identical 12V, 5W rating and W2.1x9.5d base type.
The W2.1x9.5d base specification describes a wedge-style base without pins or a bayonet fitting, relying instead on wire contacts along the sides of the glass envelope to make an electrical connection.
Although the 12961 and 12821 carry different Philips part numbers, both share the same T10 form factor, voltage, wattage, and base type, making them electrically and physically equivalent in those respects.
The 5W power rating places these bulbs in the low-wattage category typical of marker and position lighting, where output requirements are modest compared to headlamp or brake lamp circuits.