Denso Products 4171: Spark Plug, Standard, U16FSR-U, 14mm Thread, 12.70mm Reach, Flat Seat, Each - Denso standard spark plugs are designed with the smallest details in mind. Case in point: machine-rolled threads to prevent seizing or cross-threading during installation/removal. Each spark plug is 100 percent pre-fired to assure the highest possible quality. The purified alumina powder 5-rib insulator prevents flashover, provides exceptional strength, and significant thermal conductivity. The copper-glass seal cements the center electrode and insulator for a gas-tight bond. Denso standard spark plugs are available with a variety of options including projected, non-projected, and extended center electrodes, as well as rotary engine versions. Order the model recommended for your specific vehicle and engine size.