O.S. new glow plugs are designed for high nitro fuels. (25% +). Increased durability at high RPM. Durability under extreme temperatures. Allows for "leaner" needle settings for higher power and quicker throttle response. This plug is most suited for 1/8 scale, .21 Nitro-powered on-road racing. This product includes one #R5 glow plug and one brass gasket.