98066-55726 S/PLG (X16FSR-U) - Overview. The 98066-55726 S/PLG (X16FSR-U) is a genuine Honda spark plug designed specifically for Honda marine engine systems. This integral ignition component plays a critical role in the combustion process by providing the precise spark needed to ignite the fuel-air mixture reliably. Engineered for seamless integration with Honda marine engines, it ensures optimal performance, consistent starts, and fuel efficiency.. Key Features. Genuine OEM Honda spark plug en