NGK Spark Plugs & Spark Plug Caps: NGK is the undisputed leader in Motorcycle Spark Plugs, with spark plugs for virtually every Motorcycle and Scooter application in the world. Utilizing a wide variety of materials, from standard copper-core type to Iridium, NGK is the world's leader in spark plug engineering and technology. NGK Spark Plugs are specified by more motorcycle manufacturers, including Honda, Yamaha, Suzuki, and Kawasaki.