NGK Coil on Plug Boots are built to stringent OEM tolerances, combining original equipment fit, design and outstanding durability. NGK Coil on Plug Boots are manufactured using only premium silicone and always include any required internal springs and ferrite resistors for superior performance and RFI noise suppression. Bridging the important link between ignition coil and spark plug, COP boots should always be replaced with NGK Coil on Plug Boots at the time as changing spark plugs to prevent ignition problems such as flashover.