Subaru Forester Stepwell Bulb Size

Additional Notes

• The 12961 is a Philips part number designating a T10 miniature wedge bulb with a W2.1x9.5d base, rated at 12V and 5W. The wedge base design means the bulb is held in place by the socket itself rather than by pins or end caps.
• The DE3423 follows the ANSI standard used in the United States and Canada. It is a festoon-type bulb measuring 41mm in length, making contact through metal end caps at both terminals rather than through a wedge or pin base.
• The Subaru Forester stepwell position uses the 12961 across the 2014-2024 model years, with the exception of 2022, and uses the DE3423 across the 2009-2013 model years.
• The two bulb types are not interchangeable. The 12961 uses a wedge base while the DE3423 uses festoon end-cap contacts, meaning the socket design differs between the two generations of the Forester.
• Both bulb types operate on a 12V electrical system, which is standard for automotive applications. The 12961 carries an explicit 5W power rating, placing it in the low-wattage range typical of interior courtesy lighting.
• The T10 designation of the 12961 refers to the bulb's tubular envelope size, where the number indicates a width of 10 eighths of an inch. This sizing is widely used across automotive interior and parking light applications.
• The W2.1x9.5d base code of the 12961 specifies the wedge contact width and the distance between contact points, which are standardized values ensuring physical compatibility across compliant sockets.
• The festoon format of the DE3423 is common in interior dome and courtesy light positions. The 41mm length is a specific fitment requirement, as festoon bulbs of different lengths will not seat correctly in the same socket.