Spark plugs are not all alike. With the world-famous DENSO U-Groove spark plug it's easy to see, thanks to its patented U-shaped ground electrode. The U-Groove forms a channel for the spark nucleus to form at the instant of ignition, limiting quenching to generate a more potent spark. The premium features don't stop there: DENSO's distinctive five-rib insulator in purified alumina prevents leakage and flashover, while dual internal copper-glass seals and a copper-core center electrode with nickel-alloy tip assure reliable spark delivery. To keep your engine running smoothly, its spark plugs must fire 25 times a second or more. If just one spark plug skips a beat you'll know it instantly, with rough running, poor acceleration, and reduced fuel economy. DENSO U-groove spark plugs combine dependable performance and superior value.