12 V auxiliary bulb supplied in pairs, so the spare is always in the glovebox.
The NARVA T4W car bulb is a 12 V / 4 W incandescent lamp with a bayonet BA9s base, used for side markers, instrument and auxiliary lighting in 12 V vehicle systems. Each pack holds 2 bulbs, so both sides of the car can be replaced at once.
BA9s base to the ECE T4W standard
The bayonet fitting locks with a light push and twist, no tools needed. T4W is a standardised designation, so the bulb fits every socket for which the carmaker specifies T4W.
4 W at 12 V for markers and control lighting
The low current draw is easy on the vehicle's electrics during long periods of use. The roughly 8.5 mm glass envelope also fits tight reflectors and instrument panels.
Two-piece pack for replacement in pairs
Marker bulbs are best changed in pairs to keep the light output even on both sides. The second bulb can stay in the car as a spare for roadside checks and inspections.