For optimal performance and reliability, NGK LBER PLUG CAP BLUE [8308] may require resistor covers for power sport applications. These covers are designed to reduce electro magnetic and radio frequency interference, preventing misfires and poor engine performance. Made with highly durable phenolic resin and EPDM rubber ceramic resistors, they can withstand extreme heat and vibration. With this added protection, the spark plugs will have an optimal service life and performance, ensuring a smooth and efficient engine.