The NGK Iridium is considered to be the best spark plug on the market. We are offering these plugs way below their $12.95 retail price. This plug comes pre-gapped and no further gapping is necessarry, as a matter of fact you can risk plug damage if you attempt to gap them. The only difference in size is these plugs are 3/8" taller than the standard Champion plug used on Zenoah engine. These plugs are washerless and designed to be used with engines that used tapered plugs.