Prenco Coil on Plug Boot Kit (36-210804) Prenco Coil on Plug Boots are produced using precise computer designed tooling and premium quality materials/compounds that are formulated to perform in extreme temperatures. Prenco Coil on Plug Boots are designed as a direct replacement for the OE Boot. Springs, grommets and ferrite resistors are provided for all applications where applicable. Inspect and replace Coil on Plug Boots every 50,000 miles and/or with every spark plug change to ensure optimum engine efficiency and performance. Replacing Coil and Plug Boots at regular intervals will prevent/correct misfires and will help to minimize further costly damage to Ignition Coils, Sensors, Catalytic Convertors, and ECUs.