The OS Max F Glow Plug is Designed Especially for OS Max (and other brands of) Four-Stroke Engines. FEATURES: Specially shielded long-reach plug for use in four stroke engines. Shield keeps plug hot for lower idle RPM. For use with fuels with a 5-15% nitro content. INCLUDES: One #F Glow Plug (without idle bar). One brass glow plug gasket.