Mercedes-Benz C320 front and rear side marker bulbs utilize 12961 and 12821 bulb sizes respectively. The replacement chart covers 2001 through 2005 model 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 Mercedes-Benz C320 uses the 12961 bulb for the front side marker position across the 2001-2005 model years.
The rear side marker position across the same 2001-2005 model years calls for the 12821 bulb.
Both 12961 and 12821 are Philips part numbers assigned to miniature wedge bulbs of the T10 type, operating at 12 volts and rated at 5 watts.
The T10 designation refers to a tubular bulb with a nominal width of 10 thirty-seconds of an inch, a form factor widely used in low-intensity automotive lighting positions such as side markers.
Both bulbs share the W2.1x9.5d base, a wedge-type base where the electrical contacts are formed by the glass pinch at the base of the bulb rather than by a separate metal cap.
Because the 12961 and 12821 share identical electrical ratings and the same base type, the two Philips part numbers represent separate catalog entries for physically interchangeable units within the T10 wedge family.
The 5-watt rating places both bulbs in the low-wattage category typical of marker and clearance lamp applications, where illumination intensity requirements are lower than those of primary lighting functions such as headlamps or brake lamps.
The W2.1x9.5d base standard is defined by the IEC, with the numeric values indicating the contact pin width in millimeters and the overall base length in millimeters respectively, ensuring consistent fitment across compliant sockets.