RE: Spark Plug Technical Info
All Rotary engines call for this type of plug, however, there are other engines (for example, some Toyota engines) that are designed for multi-ground plugs and are not rotary engines.
A quick way to check a specific engine: use the make/model/year lookup on our site. Denso and NGK do not recommend multi-ground plugs for engines that do not call for them, even if the plug would fit. So if the results on our site list a multi-ground plug, then you know it's safe to use/recommended.