Yamaha YFM550 Grizzly FI Auto uses HS1 bulb size for both high beam and low beam headlight applications. The replacement chart covers 2009 through 2014 production specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Yamaha YFM550 Grizzly FI Auto uses the HS1 bulb type for both high beam and low beam headlights across the 2009-2014 model years.
The HS1 is a dual-filament halogen bulb, meaning a single bulb unit contains separate filaments for both high and low beam functions, which is why the same bulb size appears in both headlight positions on this vehicle.
The HS1 operates at 12 volts with a 35W/35W output rating, where the two wattage figures correspond to the low beam and high beam filaments respectively.
The HS1 bulb uses a PX43t base, a bayonet-style fitting with a specific pin configuration designed for motorcycle and powersport applications. This base type is not interchangeable with common automotive bulb bases such as H4, despite the H4 also being a dual-filament halogen bulb.
The HS1 is governed by ECE (Economic Commission for Europe) standards, a regulatory framework recognized across Europe and numerous other markets worldwide, which defines the bulb's photometric and dimensional requirements.
Because the HS1 and H4 share a similar appearance and dual-filament design, substitution errors are possible. The PX43t base on the HS1 differs from the P43t base on the H4, making the two types physically incompatible at the socket level.