Spark plugs deliver the high-voltage spark necessary to ignite the air-fuel mixture within an internal combustion engine’s cylinders. These components are used in gasoline, alcohol, and some diesel engines featuring spark ignition. Key features include electrode material (typically nickel, platinum, or iridium), heat range, and thread size, all selected to optimize combustion efficiency and longevity under specific engine conditions. Plug design variations include J-type, tapered-reach, and projected-tip to accommodate varying combustion chamber geometries. Modern spark plugs often incorporate ribbed insulators for improved dielectric strength and flame propagation. Proper gap specification is critical for reliable engine performance and is determined by engine manufacturer guidelines.