Custom lengths of Black Silicone. Annealed Fiberglass sleeve is coated with Silicone providing excellent resistance to abrasion, fraying and punctures. Resistant to chemicals and extremely flexible, heat resistant to 500°F makes it the perfect choice to cover and protect your spark plug wires. High dielectric strength for high voltage coils and ignition systems. 0.375" ID. Note: Items with custom cut patterns and/or custom cut lengths of material cannot be returned. Radiant Heat Resistance: 500°F