Nology Silver spark plugs are especially designed for high-performance engines. Silver is one of the best electrical and thermal conductors of any metal, which makes it the ultimate material for a spark plug's center electrode. The large diameter silver center electrode increases spark carrying ability and spark power. Silver is extremely resistant to erosion, guaranteeing a virtually unchanged electrode gap for the life of the spark plug. Most Nology Silver spark plugs are without a resistor, perfect for performance enthusiasts who demand the most from their engines. For racing or dependability and efficiency for everyday use, Nology Silver spark plugs deliver the most powerful spark. Sold to dealers in 4-packs.