NGK Ruthenium spark plugs for ND, set of four

Who remembers their periodic table? Ruthenium is one of those elements you don't hear about all that often, but it turns out it's a great electrode for spark plugs. It has high ignitability, meaning it gives a more complete fuel burn. This translates to a smoother idle, better cold starts and improved throttle response. It's very durable, even more so that iridium. That gives these plugs a lifespan of 80,000-100,000 miles or more.  The engineers at NGK took this precious metal and added tip designs optimized for naturally aspirated and boosted applications. The naturally aspirated plugs are gapped at 0.044" and are heat range 7, matching factory specs. The boosted plugs are gapped to 0.032" with a heat range 8 which is what we suggest for boost use. If you want to adjust the gap, please use a proper gapping tool as the tips are sensitive. Sold in sets of four, enough for one Miata (well, a four cylinder Miata).