1Fitment: The spark plug wire boots fit for fits most hot rods and classics engine, and can be matched with 90 degrees, 45 degrees straight spark plug. 2Function: Protects spark plug sheath and spark plug wires to prevent engine and exhaust overheating also improve engine performance. 3Stable Performance: Spark plug heat cover can withstand heat up to 2500F intermittent, effectively flame retardant, and protect plug wires. 4Material: This spark plug heat cover is made of basalt fiber with double layer structure for increased durability, heat insulation, high temperature resistance, safety and environmental protection. 5Easy Installation: Just slip the large end over the boot. Then carefully slip the ringed end over the boot that connects to the spark plug.