Champion RJ18YC Copper Plus Marine Spark PlugChampion marine spark plugs are quality OEM replacements. The Champion RF10C Spark Plug features a copper core electrode that provides increased conductivity and heat control for good overall wear. These marine spark plugs are designed to resist overheating under heavy engine loads.Copper Plus for dependable performanceCopper core electrode allows for accurate control of heat range for longer lifePatented TinTac and ULTRASEAL coated shell for maximum corrosion resistancePatented SAC-9 semiconductor for maximum EMI & RFI suppression.Built to ISO and SAE standards for proven performance.Champion Spark Plug # 58Application:Indmar Marine8 cyl. 350 Oldsmobile8 cyl. 403 Oldsmobile8 cyl. 455 OldsmobileVolvo Penta16A16C