Spark plug creates the electrical spark that ignites the fuel in your engine. If it's worn, your mower may not run or start at all. Keep outdoor power equipment in prime condition by Replacing spark plugs at least once every season. For faster, easier and more consistent starts, use Champion eco-clean spark plugs. Champion eco-clean is a premium small engine spark plug designed to deliver smooth starts, optimum performance and maximum plug life. Replaces RC12Y, RC14Y, BKR5E-11, E3.20, FF-20, K5RTC, and 491055. 5/8 in hex, 14mm thread, 3/4 in reach.