These plugs have a VERY fine-wire center electrode. When set at the same gap, the fine-wire requires less voltage than standard plugs to jump a spark. My mower has a 6.5 HP engine and was somewhat difficult to hand-pull fast enough to get a good spark, especially when it's cold. Of course, with no spark, no start. I installed this plug and now the mower is much easier to start. The starting rope does not have to be pulled as hard. For the last 3 mowing sessions since installing this plug, the mower has started on the first pull every time. Recommended!