Spark plug and coil with plug cap fits to premium quality petrol Water Pump 1.5inch(3.81 cm), 2hp engine. spark plug, also called Sparking Plug, device that fits into the cylinder head of an internal-combustion engine and carries two electrodes separated by an air gap, across which current from a high-tension ignition system discharges, to form a spark for igniting the air–fuel mixture.