The Autolite 26 is designed for the Kohler twin cylinder engines such as the KT17, KT19, KT21, M18, and M20 engines. Always make sure to varify your engine model. This particular spark plug will not fit the modern Kohler V twin cylinder "Command" and "Courage" engines!  The Autolite 26 uses a 14mm thread design, 15/32" reach and a tapered seat matching the cylinder head design for these particular Legacy Flathead engines.