The Ducati ST4 headlight bulb uses H9 and H1 sizes for high beam operation, with H7 and H3 sizes for low beam, representing the specific bulb requirements for this motorcycle model. The replacement chart covers 1999 through 2005 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 Ducati ST4 uses two distinct bulb configurations across its production run, with 1999-2003 models using H1 for high beam and H3 for low beam, while 2004-2005 models use H9 for high beam and H7 for low beam.
The H1 bulb is a single-filament halogen type with a P14.5s base, operating at 55 watts and designed for focused, high-intensity beam applications such as high beam headlights.
The H3 bulb is a single-filament halogen type with a PK22s base, also rated at 55 watts, and is commonly used in low beam and fog light positions where a wider light spread is required.
The H9 bulb shares the PGJ19-5 base with several other H-series types but operates at 65 watts, producing a higher lumen output than the H1 it replaced in the ST4 high beam position for 2004-2005.
The H7 bulb uses a PX26d base and is rated at 55 watts, featuring a single filament and a design that allows precise optical positioning within reflector housings, which suits the low beam role it fills in 2004-2005 models.
The base types across all four bulbs used in the ST4 are not interchangeable with one another. H1, H3, H7, and H9 each use physically distinct bases, meaning substitution between these types is not possible without modification to the housing or wiring.
Although H7 and H9 share a similar physical profile in some aftermarket contexts, their base specifications differ, and the ST4 specifications assign each to a separate function, high beam and low beam, for the 2004-2005 configuration.
The shift from H1 and H3 to H9 and H7 between the 2003 and 2004 model years represents a change in both base type and wattage for the high beam circuit, which may affect compatibility with direct-fit replacement bulbs if the incorrect year is referenced.