This is an O.S. R5 "Medium" Heat Range, Short Body Standard Glow Plug. O.S. glow plugs are designed for high nitro fuels (25% +), and increased durability at high RPM, as well as extreme temperatures. This plug allows "leaner" needle settings for higher power and quicker throttle response. This plug is best suited for 1/8 scale, .21 Nitro-powered on-road racing.