Thermo-Tec Cool-It Plug Wire Sleeves are the perfect solution if you are having issues with your headers burning up your spark plug wires and spark plugs. Increase reliability and performance by reducing potential misfires and extend spark plug and spark plug wire life. The sleeves can withstand up to 750 Degrees of conductive heat and the material is non-flammable. Available in 4 and 6 packs the spark plug wire sleeves start at 9/16" diameter at the base and flares out to 1-1/4" diameter on the spark plug side. The boots are 6" in length and available in Red, Black, Blue and Natural. Made in the U.S.A.!