ACDelco 357D GM Original Equipment Spark Plug Wire Fiberglass braid and carbon-impregnated fiberglass core for added strength and superior conductivity Spark plug distributor boot shape and materials provide proper fit, installation, and water-tight seal Terminal design improves spark plug retention and assists installation with excellent corrosion resistance Engineered for electromagnetic interference and radio frequency interference (EMI/RFI) noise suppression SAE J23031 Class E wire rating to resist heat, cold, and electrical interference