The Triumph Street Twin uses 9003 bulb size for both high beam and low beam headlight applications. Replacement chart data covers 2016 to 2018 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 9003 is a dual-filament halogen bulb, meaning a single bulb contains two separate filaments: one rated at 60W for high beam and one at 55W for low beam.
The Triumph Street Twin uses the 9003 bulb for both its high beam and low beam headlight positions across the 2016-2018 model years, with both functions served by the same physical bulb.
The 9003 operates on a 12V electrical system and uses a P43t base, which is a bayonet-style mount with a 43mm flange.
The 9003 designation is the ANSI standard used in the United States and Canada. It is electrically and physically equivalent to the H4 bulb used under international IEC standards, though the designations differ by market.
Because the 9003/H4 serves both beam functions simultaneously in a single housing, the Street Twin's headlight assembly does not require separate bulb sockets for high and low beam operation.
The P43t base is not interchangeable with single-filament bases such as P14.5s or P15d, so substitution with single-filament bulb types is not compatible with this application.